diff --git a/ez-couch.cabal b/ez-couch.cabal
--- a/ez-couch.cabal
+++ b/ez-couch.cabal
@@ -1,5 +1,5 @@
 name:               ez-couch
-version:            0.5.1
+version:            0.6.0
 cabal-version:      >=1.8
 build-type:         Simple
 license:            MIT
@@ -65,8 +65,8 @@
                     random >= 1.0,
                     resourcet >= 0.3,
                     string-conversions >= 0.2,
-                    classy-prelude >= 0.4.4,
-                    classy-prelude-conduit >= 0.4,
+                    classy-prelude >= 0.5.0,
+                    classy-prelude-conduit,
                     hashable >= 1.1,
                     vector 
 
diff --git a/src/EZCouch.hs b/src/EZCouch.hs
--- a/src/EZCouch.hs
+++ b/src/EZCouch.hs
@@ -48,6 +48,7 @@
 
   -- * Execution Monad
   MonadAction,
+  Environment,
   run,
   runWithManager,
   ConnectionSettings(..),
@@ -80,11 +81,13 @@
 import Control.Monad.Trans.Resource
 import qualified Network.HTTP.Conduit as HTTP
 
+
 runWithManager manager settings action = 
-  flip runReaderT (settings, manager) $ runResourceT $ do
-    resourceForkIO $ lift $ Sweeper.runSweeper
-    lift $ action
+  flip runReaderT (settings, manager, fromIntegral 0) $ do
+    timeDeviation <- getTimeDeviation
+    withTimeDeviation timeDeviation $ runResourceT $ do
+      resourceForkIO $ lift $ Sweeper.runSweeper
+      lift $ action
 
 run settings action = HTTP.withManager $ \manager -> 
   runWithManager manager settings action
-
diff --git a/src/EZCouch/Action.hs b/src/EZCouch/Action.hs
--- a/src/EZCouch/Action.hs
+++ b/src/EZCouch/Action.hs
@@ -10,6 +10,7 @@
 import EZCouch.Logging
 import EZCouch.Retry
 import EZCouch.Crash
+import Data.Time
 import qualified Network.HTTP.Types as HTTP
 import qualified Network.HTTP.Conduit as HTTP
 import qualified Network.HTTP.Conduit.Request as HTTP
@@ -29,11 +30,12 @@
 
 defaultPort = 5984 :: Int
 
+type Environment = (ConnectionSettings, HTTP.Manager, NominalDiffTime)
 
 -- | All EZCouch operations are performed in this monad.
-class (MonadBaseControl IO m, MonadResource m, MonadReader (ConnectionSettings, HTTP.Manager) m) => MonadAction m where
+class (MonadBaseControl IO m, MonadResource m, MonadReader Environment m) => MonadAction m where
 
-instance (MonadResource m, MonadBaseControl IO m) => MonadAction (ReaderT (ConnectionSettings, HTTP.Manager) m) 
+instance (MonadResource m, MonadBaseControl IO m) => MonadAction (ReaderT Environment m) 
 
 generateRequest :: (MonadAction m) 
   => HTTP.Method
@@ -42,7 +44,7 @@
   -> LByteString
   -> m (HTTP.Request m)
 generateRequest method dbPath qps body = do
-  (settings, _) <- ask
+  (settings, _, _) <- ask
   return $ settingsRequest settings
   where
     headers = [("Content-Type", "application/json")]
@@ -71,12 +73,12 @@
   logLn 0 $ "Performing a " 
     ++ show (HTTP.method request) 
     ++ " at " ++ show (HTTP.url request)
-  (_, manager) <- ask
+  (_, manager, _) <- ask
   retrying exceptionIntervals $ 
     processResponse =<< http' request manager
   where
-    exceptionIntervals (ConnectionException {}) = [10^3, 10^6, 10^6*10]
-    exceptionIntervals (ServerException {}) = [10^3, 10^6, 10^6*10]
+    exceptionIntervals (ConnectionException {}) = map (*10^6) [0, 1, 5]
+    exceptionIntervals (ServerException {}) = map (*10^6) [0, 1, 5]
     exceptionIntervals _ = []
 
 http' request manager = 
@@ -138,7 +140,7 @@
         Aeson.Success _ -> 
           throwIO $ ServerException $ "Status " ++ show code ++ " response: " ++ (decodeUtf8 . toStrict . Aeson.encode) json
         Aeson.Error m -> 
-          crash $ (pack) m ++ ". Response body: " ++ (toStrict . decodeUtf8 . Aeson.encode) json
+          throwIO $ ServerException $ "Status " ++ show code
     _ | code >= 400 ->
       crash $ "Unexpected status code: " ++ show code ++ ", " ++ (decodeUtf8) msg
     _ -> return $ ResponseOk response
diff --git a/src/EZCouch/Parsing.hs b/src/EZCouch/Parsing.hs
--- a/src/EZCouch/Parsing.hs
+++ b/src/EZCouch/Parsing.hs
@@ -3,8 +3,6 @@
 
 import Prelude ()
 import ClassyPrelude
-import Control.Monad.Trans.Resource
-import qualified Data.Text.Lazy as Text
 import EZCouch.Types
 import Data.Aeson as Aeson 
 
@@ -16,12 +14,12 @@
 rowsParser1 :: Parser (Vector Aeson.Value)
 rowsParser1 json
   | Just (Aeson.Array rows) <- json .? "rows" = Right rows
-  | otherwise = Left $ unexpectedJSONValue json
+  | otherwise = Left $ unexpectedJSONValue "rowsParser1" json
 
 rowsParser2 :: Parser (Vector Aeson.Value)
 rowsParser2 json
   | Aeson.Array rows <- json = Right rows
-  | otherwise = Left $ unexpectedJSONValue json
+  | otherwise = Left $ unexpectedJSONValue "rowsParser2" json
 
 idRevParser :: Parser (Text, Maybe Text)
 idRevParser o @ (Aeson.Object m) 
@@ -33,7 +31,7 @@
     Just id <- lookup "id" m
     = (,) <$> fromJSON' id <*> pure Nothing
   | otherwise
-    = Left $ unexpectedJSONValue o
+    = Left $ unexpectedJSONValue "idRevParser" o
 
 keyExistsParser :: (FromJSON k) => Parser (k, Bool)
 keyExistsParser o @ (Aeson.Object m) 
@@ -49,7 +47,7 @@
     Just key <- lookup "key" m
     = (,) <$> fromJSON' key <*> pure True
   | otherwise
-    = Left $ unexpectedJSONValue o
+    = Left $ unexpectedJSONValue "keyExistsParser" o
 
 persistedParser :: (FromJSON a) => Parser (Maybe (Persisted a))
 persistedParser o
@@ -59,8 +57,10 @@
     Just doc <- o .? "doc",
     Just rev <- doc .? "_rev"
     = fmap Just $ Persisted <$> fromJSON' id <*> fromJSON' rev <*> fromJSON' doc
+  | o .? "doc" == Just Aeson.Null
+    = Right Nothing
   | otherwise
-    = Left $ unexpectedJSONValue o
+    = Left $ unexpectedJSONValue "persistedParser" o
 
 errorPersistedParser :: (FromJSON a) => Parser (Either (Text, Text) (Persisted a))
 errorPersistedParser o @ (Aeson.Object m) 
@@ -70,7 +70,7 @@
   | Just error <- lookup "error" m, Just reason <- lookup "reason" m
     = fmap Left $ (,) <$> fromJSON' error <*> fromJSON' reason 
   | otherwise
-    = Left $ unexpectedJSONValue o
+    = Left $ unexpectedJSONValue "errorPersistedParser" o
 
 maybePersistedByKeyParser :: (FromJSON a, FromJSON k) => Parser (k, Maybe (Persisted a))
 maybePersistedByKeyParser o @ (Aeson.Object m) 
@@ -94,7 +94,7 @@
     Just key <- lookup "key" m
     = (,) <$> fromJSON' key <*> pure Nothing
   | otherwise
-    = Left $ unexpectedJSONValue o
+    = Left $ unexpectedJSONValue "maybePersistedByKeyParser" o
 
 
 
@@ -103,10 +103,12 @@
   Aeson.Error s -> Left $ "fromJSON failed with a message `" 
     ++ fromString s 
     ++ "` on the following value: " 
-    ++ (Text.toStrict . decodeUtf8 $ Aeson.encode json) 
+    ++ (toStrict . decodeUtf8 $ Aeson.encode json) 
 
-unexpectedJSONValue json = 
-  "Unexpected JSON value: " ++ (Text.toStrict . decodeUtf8 $ Aeson.encode json)
+unexpectedJSONValue parserName json = 
+  parserName ++ ": "
+    ++ "Unexpected JSON value: " 
+    ++ (toStrict . decodeUtf8 $ Aeson.encode json)
 
 o .? k = pure o ?.? k
 o ?.? k = o >>= objectKey k
diff --git a/src/EZCouch/Retry.hs b/src/EZCouch/Retry.hs
--- a/src/EZCouch/Retry.hs
+++ b/src/EZCouch/Retry.hs
@@ -7,16 +7,6 @@
 import EZCouch.Logging
 
 
-retryingEither [] action = action 
-retryingEither (i:is) action = action >>= processResult
-  where 
-    processResult (Left _) 
-      | i == 0 = retryingEither is action
-      | otherwise = liftIO (threadDelay i) >> retryingEither is action
-    processResult r = return r
-
-retryingEither' = retryingEither defaultIntervals
-
 retrying exceptionIntervals action = retrying_ 0
   where
     retrying_ attempt = catch action processException
diff --git a/src/EZCouch/Time.hs b/src/EZCouch/Time.hs
--- a/src/EZCouch/Time.hs
+++ b/src/EZCouch/Time.hs
@@ -6,14 +6,18 @@
 import System.Locale
 import Data.Time
 import qualified Network.HTTP.Types as HTTP
-
+import Control.Monad.Reader
 import EZCouch.Types
 import EZCouch.Action
 
--- | Current time according to server.
+-- | Current time according to server. This function doesn't actually emit any
+-- requests to the server, calculating the value from a deviation of local time
+-- from server time determined at the beginning of the EZCouch session.
 readTime :: MonadAction m => m UTCTime 
-readTime = getResponseHeaders HTTP.methodGet mempty mempty mempty
-  >>= getHeadersTime
+readTime = do
+  (_, _, deviation) <- ask
+  localTime <- liftIO $ getCurrentTime
+  return $ addUTCTime deviation localTime
 
 getHeadersTime ((name, value) : tail) 
   | name == HTTP.hDate = case toTime value of
@@ -24,3 +28,14 @@
 
 toTime = parseTime defaultTimeLocale "%a, %d %b %Y %H:%M:%S %Z" 
   . unpack . asText . decodeUtf8
+
+getTimeDeviation :: MonadAction m => m NominalDiffTime 
+getTimeDeviation = do
+  dbTime <- getResponseHeaders HTTP.methodGet mempty mempty mempty
+    >>= getHeadersTime
+  localTime <- liftIO $ getCurrentTime
+  return $ diffUTCTime dbTime localTime
+
+withTimeDeviation :: (MonadAction m) => NominalDiffTime -> m a -> m a
+withTimeDeviation timeDeviation =
+  local (\(settings, manager, _) -> (settings, manager, timeDeviation)) 
diff --git a/src/EZCouch/WriteAction.hs b/src/EZCouch/WriteAction.hs
--- a/src/EZCouch/WriteAction.hs
+++ b/src/EZCouch/WriteAction.hs
@@ -61,7 +61,7 @@
 
 createIdentifiedEntities :: (MonadAction m, ToJSON a) 
   => [Identified a]
-  -> m [Either (Text, a) (Persisted a)]
+  -> m [Either (Identified a) (Persisted a)]
 createIdentifiedEntities idsToVals 
   = writeOperationsAction [Create id val | (id, val) <- idsToVals]
       >>= mapM convertResult
@@ -118,4 +118,4 @@
     
 lookupThrowing id cache = case lookup id cache of
   Just val -> return val
-  Nothing -> throwIO $ ParsingException $ "Unexpected id: " ++ show id
+  Nothing -> throwIO $ ResponseException $ "Unexpected id: " ++ show id