diff --git a/hakyll.cabal b/hakyll.cabal
--- a/hakyll.cabal
+++ b/hakyll.cabal
@@ -1,5 +1,5 @@
 Name:               hakyll
-Version:            2.1
+Version:            2.1.1
 
 Synopsis:           A simple static site generator library.
 Description:        A simple static site generator library, mainly aimed at
diff --git a/src/Network/Hakyll/SimpleServer.hs b/src/Network/Hakyll/SimpleServer.hs
--- a/src/Network/Hakyll/SimpleServer.hs
+++ b/src/Network/Hakyll/SimpleServer.hs
@@ -102,7 +102,8 @@
 createGetResponse request = do
     -- Construct the complete fileName of the requested resource.
     config <- ask
-    let uri = requestURI request
+    let -- Drop everything after a '?'.
+        uri = takeWhile ((/=) '?') $ requestURI request
         log' = writeChan (logChannel config)
     isDirectory <- liftIO $ doesDirectoryExist $ documentRoot config ++ uri
     let fileName =
@@ -187,8 +188,12 @@
 
 -- | Start a simple http server on the given 'PortNumber', serving the given
 --   directory.
-simpleServer :: PortNumber -> FilePath -> IO ()
-simpleServer port root = do
+--
+simpleServer :: PortNumber  -- ^ Port to listen on.
+             -> FilePath    -- ^ Root directory to serve.
+             -> IO ()       -- ^ Optional pre-respond action.
+             -> IO ()
+simpleServer port root preRespond = do
     -- Channel to send logs to
     logChan <- newChan
 
@@ -199,6 +204,7 @@
 
           -- When a client connects, respond in a separate thread.
         listen socket = do (handle, _, _) <- accept socket
+                           preRespond
                            forkIO (runReaderT (respond handle) config)
 
     -- Handle logging in a separate thread
diff --git a/src/Text/Hakyll.hs b/src/Text/Hakyll.hs
--- a/src/Text/Hakyll.hs
+++ b/src/Text/Hakyll.hs
@@ -1,4 +1,4 @@
--- | This is the main Hakyll module, exporting the important @hakyl@ function.
+-- | This is the main Hakyll module, exporting the important @hakyll@ function.
 --
 --   Most configurations would use this @hakyll@ function more or less as the
 --   main function:
@@ -14,20 +14,18 @@
     ) where
 
 import Control.Monad.Reader (runReaderT, liftIO, ask)
-import Control.Concurrent (forkIO, threadDelay)
 import Control.Monad (when)
 import qualified Data.Map as M
 import System.Environment (getArgs, getProgName)
 import System.Directory (doesDirectoryExist, removeDirectoryRecursive)
-import System.Time (getClockTime)
 
 import Text.Pandoc
 
 import Network.Hakyll.SimpleServer (simpleServer)
 import Text.Hakyll.HakyllMonad
-import Text.Hakyll.File
 
 -- | The default reader options for pandoc parsing.
+--
 defaultPandocParserState :: ParserState
 defaultPandocParserState = defaultParserState
     { -- The following option causes pandoc to read smart typography, a nice
@@ -36,6 +34,7 @@
     }
 
 -- | The default writer options for pandoc rendering.
+--
 defaultPandocWriterOptions :: WriterOptions
 defaultPandocWriterOptions = defaultWriterOptions
     { -- This option causes literate haskell to be written using '>' marks in
@@ -44,6 +43,7 @@
     }
 
 -- | The default hakyll configuration.
+--
 defaultHakyllConfiguration :: HakyllConfiguration
 defaultHakyllConfiguration = HakyllConfiguration
     { absoluteUrl         = ""
@@ -51,14 +51,14 @@
     , siteDirectory       = "_site"
     , cacheDirectory      = "_cache"
     , enableIndexUrl      = False
-    , previewPollDelay    = 1000000
     , pandocParserState   = defaultPandocParserState
     , pandocWriterOptions = defaultPandocWriterOptions
     }
 
 -- | Main function to run Hakyll with the default configuration. The
---   absolute URL is only used in certain cases, for example RSS feeds et
---   cetera.
+-- absolute URL is only used in certain cases, for example RSS feeds et
+-- cetera.
+--
 hakyll :: String    -- ^ Absolute URL of your site. Used in certain cases.
        -> Hakyll () -- ^ You code.
        -> IO ()
@@ -67,20 +67,22 @@
     configuration = defaultHakyllConfiguration { absoluteUrl = absolute }
 
 -- | Main function to run hakyll with a custom configuration.
+--
 hakyllWithConfiguration :: HakyllConfiguration -> Hakyll () -> IO ()
 hakyllWithConfiguration configuration buildFunction = do
     args <- getArgs
     let f = case args of ["build"]      -> buildFunction
                          ["clean"]      -> clean
-                         ["preview", p] -> preview buildFunction (read p)
-                         ["preview"]    -> preview buildFunction 8000
+                         ["preview", p] -> server (read p) buildFunction
+                         ["preview"]    -> server 8000 buildFunction
                          ["rebuild"]    -> clean >> buildFunction
-                         ["server", p]  -> server (read p)
-                         ["server"]     -> server 8000
+                         ["server", p]  -> server (read p) (return ())
+                         ["server"]     -> server 8000 (return ())
                          _              -> help
     runReaderT f configuration
 
 -- | Clean up directories.
+--
 clean :: Hakyll ()
 clean = do askHakyll siteDirectory >>= remove'
            askHakyll cacheDirectory >>= remove'
@@ -89,24 +91,8 @@
                               exists <- doesDirectoryExist dir
                               when exists $ removeDirectoryRecursive dir
 
--- | Autocompile mode.
-preview :: Hakyll () -> Integer -> Hakyll ()
-preview buildFunction port = do
-    buildFunction
-    _ <- startServer
-    liftIO getClockTime >>= run
-  where
-    startServer = do configuration <- ask
-                     liftIO $ forkIO $ runReaderT (server port) configuration
-    run time = do delay <- askHakyll previewPollDelay
-                  liftIO $ threadDelay delay
-                  contents <- getRecursiveContents "."
-                  valid <- isMoreRecent time contents
-                  if valid then run time
-                           else do buildFunction
-                                   liftIO getClockTime >>= run
-
 -- | Show usage information.
+--
 help :: Hakyll ()
 help = liftIO $ do
     name <- getProgName
@@ -122,5 +108,12 @@
              ++ name ++ " server [port]   Run a local test server.\n"
 
 -- | Start a server at the given port number.
-server :: Integer -> Hakyll ()
-server p = askHakyll siteDirectory >>= liftIO . simpleServer (fromIntegral p)
+--
+server :: Integer    -- ^ Port number to serve on.
+       -> Hakyll ()  -- ^ Pre-respond action.
+       -> Hakyll ()
+server port preRespond = do 
+    configuration <- ask
+    root <- askHakyll siteDirectory
+    let preRespondIO = runReaderT preRespond configuration
+    liftIO $ simpleServer (fromIntegral port) root preRespondIO
diff --git a/src/Text/Hakyll/ContextManipulations.hs b/src/Text/Hakyll/ContextManipulations.hs
--- a/src/Text/Hakyll/ContextManipulations.hs
+++ b/src/Text/Hakyll/ContextManipulations.hs
@@ -3,12 +3,14 @@
 module Text.Hakyll.ContextManipulations
     ( renderValue
     , changeValue
+    , changeUrl
     , copyValue
     , renderDate
     , changeExtension
     , renderBody
     ) where
 
+import Control.Monad (liftM)
 import Control.Arrow (arr)
 import System.Locale (defaultTimeLocale)
 import System.FilePath (takeFileName, addExtension, dropExtension)
@@ -18,7 +20,7 @@
 import qualified Data.Map as M
 
 import Text.Hakyll.Regex (substituteRegex)
-import Text.Hakyll.HakyllAction (HakyllAction)
+import Text.Hakyll.HakyllAction (HakyllAction (..))
 import Text.Hakyll.Context (Context)
 
 -- | Do something with a value in a @Context@, but keep the old value as well.
@@ -42,6 +44,14 @@
             -> (String -> String) -- ^ Function to apply on the value.
             -> HakyllAction Context Context
 changeValue key = renderValue key key
+
+-- | Change the URL of a page. This requires a special function, so dependency
+-- handling can happen correctly.
+-- 
+changeUrl :: (String -> String)            -- ^ Function to change URL with.
+          -> HakyllAction Context Context  -- ^ Resulting action.
+changeUrl f = let action = changeValue "url" f
+              in action {actionUrl = Right $ liftM f}
 
 -- | Copy a value from one key to another in a @Context@.
 copyValue :: String -- ^ Source key.
diff --git a/src/Text/Hakyll/CreateContext.hs b/src/Text/Hakyll/CreateContext.hs
--- a/src/Text/Hakyll/CreateContext.hs
+++ b/src/Text/Hakyll/CreateContext.hs
@@ -11,7 +11,7 @@
 
 import qualified Data.Map as M
 import Control.Arrow (second)
-import Control.Monad (liftM2, mplus)
+import Control.Monad (liftM2)
 import Control.Applicative ((<$>))
 
 import Text.Hakyll.File
@@ -25,7 +25,7 @@
 createPage :: FilePath -> HakyllAction () Context
 createPage path = HakyllAction
     { actionDependencies = [path]
-    , actionUrl          = Just $ toUrl path
+    , actionUrl          = Left $ toUrl path
     , actionFunction     = const (readPage path)
     }
 
@@ -41,7 +41,7 @@
                  -> HakyllAction () Context
 createCustomPage url association = HakyllAction
     { actionDependencies = dataDependencies
-    , actionUrl          = Just $ return url
+    , actionUrl          = Left $ return url
     , actionFunction     = \_ -> M.fromList <$> assoc'
     }
   where
@@ -78,7 +78,7 @@
         -> HakyllAction () Context
 combine x y = HakyllAction
     { actionDependencies = actionDependencies x ++ actionDependencies y
-    , actionUrl          = actionUrl x `mplus` actionUrl y
+    , actionUrl          = actionUrl x
     , actionFunction     = \_ ->
         liftM2 M.union (runHakyllAction x) (runHakyllAction y)
     }
@@ -90,7 +90,7 @@
                -> HakyllAction () Context
                -> HakyllAction () Context
 combineWithUrl url x y = combine'
-    { actionUrl          = Just $ return url
+    { actionUrl          = Left $ return url
     , actionFunction     = \_ -> M.insert "url" url <$> runHakyllAction combine'
     }
   where
diff --git a/src/Text/Hakyll/HakyllAction.hs b/src/Text/Hakyll/HakyllAction.hs
--- a/src/Text/Hakyll/HakyllAction.hs
+++ b/src/Text/Hakyll/HakyllAction.hs
@@ -11,7 +11,7 @@
 
 import Control.Arrow
 import Control.Category
-import Control.Monad ((<=<), mplus, unless)
+import Control.Monad ((<=<), unless)
 import Control.Monad.Reader (liftIO)
 import Prelude hiding ((.), id)
 import System.IO (hPutStrLn, stderr)
@@ -24,7 +24,8 @@
     { -- | Dependencies of the @HakyllAction@.
       actionDependencies :: [FilePath]
     , -- | URL pointing to the result of this @HakyllAction@.
-      actionUrl          :: Maybe (Hakyll FilePath)
+      actionUrl          :: Either (Hakyll FilePath)
+                                   (Hakyll FilePath -> Hakyll FilePath)
     , -- | The actual render function.
       actionFunction     :: a -> Hakyll b
     }
@@ -45,7 +46,7 @@
                        -> HakyllAction () b -- ^ The resulting action.
 createFileHakyllAction path action = HakyllAction
     { actionDependencies = [path]
-    , actionUrl          = Just $ return path
+    , actionUrl          = Left $ return path
     , actionFunction     = const action
     }
 
@@ -60,8 +61,8 @@
                         -> Hakyll ()          -- ^ Empty result.
 runHakyllActionIfNeeded action = do
     url <- case actionUrl action of
-        (Just u) -> u
-        Nothing  -> error "No url when checking dependencies."
+        Left u  -> u
+        Right _ -> error "No url when checking dependencies."
     destination <- toDestination url
     valid <- isFileMoreRecent destination $ actionDependencies action
     unless valid $ do liftIO $ hPutStrLn stderr $ "Rendering " ++ destination
@@ -76,13 +77,17 @@
 instance Category HakyllAction where
     id = HakyllAction
         { actionDependencies = []
-        , actionUrl          = Nothing
+        , actionUrl          = Right id
         , actionFunction     = return
         }
 
     x . y = HakyllAction
         { actionDependencies = actionDependencies x ++ actionDependencies y
-        , actionUrl          = actionUrl x `mplus` actionUrl y
+        , actionUrl          = case actionUrl x of
+            Left ux  -> Left ux
+            Right fx -> case actionUrl y of
+                Left uy  -> Left (fx uy)
+                Right fy -> Right (fx . fy)
         , actionFunction     = actionFunction x <=< actionFunction y
         }
 
diff --git a/src/Text/Hakyll/HakyllMonad.hs b/src/Text/Hakyll/HakyllMonad.hs
--- a/src/Text/Hakyll/HakyllMonad.hs
+++ b/src/Text/Hakyll/HakyllMonad.hs
@@ -30,8 +30,6 @@
       cacheDirectory      :: FilePath
     , -- | Enable index links.
       enableIndexUrl      :: Bool
-    , -- | Delay between polls in preview mode.
-      previewPollDelay    :: Int
     , -- | Pandoc parsing options
       pandocParserState   :: ParserState
     , -- | Pandoc writer options
diff --git a/src/Text/Hakyll/Paginate.hs b/src/Text/Hakyll/Paginate.hs
--- a/src/Text/Hakyll/Paginate.hs
+++ b/src/Text/Hakyll/Paginate.hs
@@ -61,8 +61,8 @@
   where
     -- Create a link with a given label, taken from the configuration.
     linkWithLabel f r = Right $ case actionUrl r of
-        Just l  -> createSimpleHakyllAction $ link (f configuration) <$> l
-        Nothing -> error "No link found for pagination."
+        Left l  -> createSimpleHakyllAction $ link (f configuration) <$> l
+        Right _ -> error "No link found for pagination."
 
     -- The main function that creates combined renderables by recursing over
     -- the list of items.
diff --git a/src/Text/Hakyll/Render.hs b/src/Text/Hakyll/Render.hs
--- a/src/Text/Hakyll/Render.hs
+++ b/src/Text/Hakyll/Render.hs
@@ -40,7 +40,7 @@
        -> HakyllAction Context Context -- ^ The render computation.
 render templatePath = HakyllAction
     { actionDependencies = [templatePath]
-    , actionUrl          = Nothing
+    , actionUrl          = Right id
     , actionFunction     = \context ->
         flip pureRender context <$> readTemplate templatePath
     }
@@ -59,7 +59,7 @@
                 -> HakyllAction () String
 renderAndConcat templatePaths renderables = HakyllAction
     { actionDependencies = renders >>= actionDependencies
-    , actionUrl          = Nothing
+    , actionUrl          = Right id
     , actionFunction     = actionFunction'
     }
   where
diff --git a/src/Text/Hakyll/Tags.hs b/src/Text/Hakyll/Tags.hs
--- a/src/Text/Hakyll/Tags.hs
+++ b/src/Text/Hakyll/Tags.hs
@@ -68,7 +68,7 @@
         -> HakyllAction () TagMap
 readMap getTagsFunction identifier paths = HakyllAction
     { actionDependencies = paths
-    , actionUrl          = Nothing
+    , actionUrl          = Right id
     , actionFunction     = actionFunction'
     } 
   where