diff --git a/BuildBox.hs b/BuildBox.hs
--- a/BuildBox.hs
+++ b/BuildBox.hs
@@ -7,7 +7,9 @@
         , runBuildWithState
 
         -- * Errors
+        , BuildError    (..)
         , throw
+        , catch
         , needs
 
         -- * Utils
@@ -18,3 +20,4 @@
         , outLn)
 where
 import BuildBox.Build
+import Prelude          hiding (catch)
diff --git a/BuildBox/Build.hs b/BuildBox/Build.hs
--- a/BuildBox/Build.hs
+++ b/BuildBox/Build.hs
@@ -2,7 +2,6 @@
 -- | Defines the main `Build` monad and common utils.
 module BuildBox.Build 
 	( module BuildBox.Build.Testable
-	, module BuildBox.Build.BuildError
 	, module BuildBox.Build.BuildState
 	, Build
 
@@ -14,7 +13,9 @@
 	, successfully
 
 	-- * Errors
+        , BuildError    (..)
 	, throw
+        , catch
 	, needs
 
 	-- * Utils
@@ -36,7 +37,7 @@
 import BuildBox.Build.BuildError
 import Control.Monad.State
 import System.IO
-
+import Prelude                  hiding (catch)
 
 -- | Log a system command to the handle in our `BuildConfig`, if any.
 logSystem :: String -> Build ()
diff --git a/BuildBox/Build/Base.hs b/BuildBox/Build/Base.hs
--- a/BuildBox/Build/Base.hs
+++ b/BuildBox/Build/Base.hs
@@ -82,6 +82,17 @@
 throw	= throwError
 
 
+-- | Run a build command, catching any exceptions it sends.
+catch :: Build a -> (BuildError -> Build a) -> Build a
+catch build handle
+ = do   s            <- get
+        (result, s') <- io $ runStateT (runErrorT build) s
+        case result of
+         Left err -> handle err
+         Right x  
+          -> do put s'
+                return x
+
 -- | Throw a needs error saying we needs the given file.
 --   A catcher could then usefully create the file, or defer the compuation until it has been 
 --   created.
diff --git a/BuildBox/Build/BuildError.hs b/BuildBox/Build/BuildError.hs
--- a/BuildBox/Build/BuildError.hs
+++ b/BuildBox/Build/BuildError.hs
@@ -46,21 +46,25 @@
 
 	ErrorSystemCmdFailed{}
 	 -> vcat 
-		[ text "System command failure."
+	 $ 	[ text "System command failure."
 		, text "    command: " <> (text $ buildErrorCmd err)
 		, text "  exit code: " <> (text $ show $ buildErrorCode err)
-		, blank
-		, if (not $ Log.null $ buildErrorStdout err)
-		   then vcat 	[ text "-- stdout (last 10 lines) ------------------------------------------------------"
-				, text $ Log.toString $ Log.lastLines 10 $ buildErrorStdout err]
-		   else text ""
-		, blank
-		, if (not $ Log.null $ buildErrorStderr err)
-		   then vcat	[ text "-- stderr (last 10 lines) ------------------------------------------------------"
-				, text $ Log.toString $ Log.lastLines 10 $ buildErrorStderr err]
-		   else text ""
-		
-		, 		  text "--------------------------------------------------------------------------------" ]
+		, blank ] 
+
+         ++ (if (not $ Log.null $ buildErrorStdout err)
+	     then [ text "-- stdout (last 10 lines) ------------------------------------------------------"
+		  , text $ Log.toString $ Log.lastLines 10 $ buildErrorStdout err]
+	     else [])
+
+         ++ (if (not $ Log.null $ buildErrorStderr err)
+	     then [ text "-- stderr (last 10 lines) ------------------------------------------------------"
+		  , text $ Log.toString $ Log.lastLines 10 $ buildErrorStderr err ]
+	     else [])
+
+	 ++ (if (  (not $ Log.null $ buildErrorStdout err)
+               || (not $ Log.null $ buildErrorStderr err))
+             then [ text "--------------------------------------------------------------------------------" ]
+             else [])
 	
 	ErrorIOError ioerr
 	 -> text "IO error: " <> (text $ show ioerr)
diff --git a/BuildBox/Command/Environment.hs b/BuildBox/Command/Environment.hs
--- a/BuildBox/Command/Environment.hs
+++ b/BuildBox/Command/Environment.hs
@@ -106,7 +106,7 @@
 getHostName :: Build String
 getHostName
  = do	check $ HasExecutable "uname"
-	name	<- qssystemOut "uname -n"
+	name   <- sesystemq "uname -n"
 	return	$ init name
 
 
@@ -114,7 +114,7 @@
 getHostArch :: Build String
 getHostArch
  = do	check $ HasExecutable "arch"
-	name	<- qssystemOut "arch"
+	name   <- sesystemq "arch"
 	return	$ init name
 
 
@@ -122,7 +122,7 @@
 getHostProcessor :: Build String
 getHostProcessor
  = do	check $ HasExecutable "uname"
-	name	<- qssystemOut "uname -p"
+	name   <- sesystemq "uname -p"
 	return	$ init name
 
 
@@ -130,15 +130,15 @@
 getHostOS :: Build String
 getHostOS
  = do	check $ HasExecutable "uname"
-	os	<- qssystemOut "uname -s"
-	return	$ init os
+	name   <- sesystemq "uname -s"
+	return	$ init name
 
 
 -- | Get the host operating system release, using @uname@.
 getHostRelease :: Build String
 getHostRelease
  = do	check $ HasExecutable "uname"
-	str	<- qssystemOut "uname -r"
+	str    <- sesystemq "uname -r"
 	return	$ init str
 
 
@@ -147,14 +147,14 @@
 getVersionGHC :: FilePath -> Build String
 getVersionGHC path
  = do	check $ HasExecutable path
-	str	<- qssystemOut $ path ++ " --version"
+	str	<- sesystemq $ path ++ " --version"
 	return	$ init str
 	
 -- | Get the version of this GCC, or throw an error if it can't be found. 
 getVersionGCC :: FilePath -> Build String
 getVersionGCC path
  = do	check $ HasExecutable path
- 	str	<- qssystemOut $ path ++ " --version"
+ 	str	<- sesystemq $ path ++ " --version"
 	return	$ head $ lines str
 
 
diff --git a/BuildBox/Command/File.hs b/BuildBox/Command/File.hs
--- a/BuildBox/Command/File.hs
+++ b/BuildBox/Command/File.hs
@@ -35,7 +35,7 @@
  test prop
   = case prop of
 	HasExecutable name
-	 -> do	code	<- qsystem $ "which " ++ name
+	 -> do	(code, _, _) <- systemq $ "which " ++ name
 		return	$ code == ExitSuccess
 
 	HasFile path
@@ -70,10 +70,10 @@
 	-- Make sure a dir with this name doesn't already exist.
 	checkFalse $ HasDir name
 
-	ssystem $ "mkdir -p " ++ name                                          -- TODO: rewrite without shell options
+	ssystem $ "mkdir -p " ++ name               -- TODO: rewrite without shell options
 	x	<- inDir name build
 
-	ssystem $ "rm -Rf " ++ name                                            -- TODO: rewrite without shell opts
+	ssystem $ "rm -Rf " ++ name                 -- TODO: rewrite without shell opts
 	return x
 
 
@@ -82,8 +82,8 @@
 --   not follow symlinks, it just deletes them.
 clobberDir :: FilePath -> Build ()
 clobberDir path
- = 	ssystem $ "rm -Rf " ++ path                                         -- TODO: rewrite without shell opts
-
+ = do   ssystemq $ "rm -Rf " ++ path                 -- TODO: rewrite without shell opts
+        return ()
 
 -- | Create a new directory if it isn't already there, or return successfully if it is.
 ensureDir :: FilePath -> Build ()
@@ -91,7 +91,8 @@
  = do	already	<- io $ doesDirectoryExist path
 	if already
 	 then return ()
-	 else ssystem $ "mkdir -p " ++ path                                    -- TODO: rewrite without shell opts
+	 else do ssystemq $ "mkdir -p " ++ path         -- TODO: rewrite without shell opts
+                 return ()
 
 
 -- | Create a temp file, pass it to some command, then delete the file after the command finishes.
@@ -122,7 +123,8 @@
         ensureDir buildDir
 
 	-- Build the file name we'll try to use.
-	let fileName	 = buildDir ++ "/buildbox-" ++ show buildId ++ "-" ++ show buildSeq       -- TODO: normalise path
+	let fileName	 = buildDir ++ "/buildbox-" ++ show buildId ++ "-" ++ show buildSeq       
+                                                -- TODO: normalise path
 
 	-- If it already exists then something has gone badly wrong.
 	--   Maybe the unique Id for the process wasn't as unique as we thought.
@@ -143,4 +145,5 @@
 atomicWriteFile filePath str
  = do	tmp	<- newTempFile
 	io $ writeFile tmp str
-	ssystem $ "mv " ++ tmp ++ " " ++ filePath
+	ssystemq $ "mv " ++ tmp ++ " " ++ filePath
+        return ()
diff --git a/BuildBox/Command/Mail.hs b/BuildBox/Command/Mail.hs
--- a/BuildBox/Command/Mail.hs
+++ b/BuildBox/Command/Mail.hs
@@ -1,6 +1,8 @@
 
--- | Sending email. We've got baked in support for @msmtp@, which is easy to set up. Adding support for other mailers 
---   should be easy. Get @msmtp@ here: <http://msmtp.sourceforge.net>
+-- | Sending email. 
+--   If you're on a system with a working @sendmail@ then use that.
+--   Otherwise, the stand-alone @msmtp@ server is easy to set up.
+--   Get @msmtp@ here: <http://msmtp.sourceforge.net>
 module BuildBox.Command.Mail
 	( Mail(..)
 	, Mailer(..)
@@ -54,7 +56,7 @@
 -- | Create a mail with a given from, to, subject and body.
 --   Fill in the date and message id based on the current time.
 --   Valid dates and message ids are needed to prevent the mail
---   being bounced by spambots.
+--   being bounced by anti-spam systems.
 createMailWithCurrentTime 
 	:: String 	-- ^ ''from'' field. Should be an email address.
 	-> String	-- ^ ''to'' field. Should be an email address.
diff --git a/BuildBox/Command/Network.hs b/BuildBox/Command/Network.hs
--- a/BuildBox/Command/Network.hs
+++ b/BuildBox/Command/Network.hs
@@ -29,7 +29,7 @@
 	-- -o               exit successfully after recieving one reply packet.
 	HostReachable hostName
 	 -> do	check	$ HasExecutable "ping"
-		code	<- qsystem $ "ping -o " ++ hostName
+		(code, _, _) <- systemq $ "ping -o " ++ hostName
 		return $ code == ExitSuccess
 		
 	-- Works on OSX 10.6.2, wget 1.12
@@ -37,7 +37,7 @@
 	--  --delete-after  delete page after downloading.
 	UrlGettable url
 	 -> do	check	$ HasExecutable "wget"
-		code 	<- qsystem $ "wget -q --delete-after " ++ url
+		(code, _, _) <- systemq $ "wget -q --delete-after " ++ url
 		return	$ code == ExitSuccess
 		
 
diff --git a/BuildBox/Command/System.hs b/BuildBox/Command/System.hs
--- a/BuildBox/Command/System.hs
+++ b/BuildBox/Command/System.hs
@@ -12,11 +12,11 @@
 
 	-- * Wrappers
 	, system
+	, systemq
 	, ssystem
-	, qsystem
-	, qssystem
-	, ssystemOut
-	, qssystemOut
+	, ssystemq
+	, sesystem
+	, sesystemq
 	, systemTee
 	, systemTeeLog
 	, ssystemTee
@@ -46,46 +46,55 @@
 
 
 -- Wrappers ---------------------------------------------------------------------------------------
--- | Run a system command, returning its exit code.
-system :: String -> Build ExitCode
+-- | Run a system command, 
+--   returning its exit code and what it wrote to @stdout@ and @stderr@.
+system :: String -> Build (ExitCode, String, String)
 system cmd
- = do	(code, _, _)		<- systemTeeLog True cmd Log.empty
-	return code
+ = do	(code, logOut, logErr)    <- systemTeeLog True cmd Log.empty
+	return (code, Log.toString logOut, Log.toString logErr)
 
 
--- | Run a successful system command.
+-- | Quietly run a system command,
+--   returning its exit code and what it wrote to @stdout@ and @stderr@.
+systemq :: String -> Build (ExitCode, String, String)
+systemq cmd
+ = do	(code, logOut, logErr)    <- systemTeeLog False cmd Log.empty
+        return (code, Log.toString logOut, Log.toString logErr)
+
+
+
+-- | Run a successful system command, 
+--   returning what it wrote to @stdout@ and @stderr@.
 --   If the exit code is `ExitFailure` then throw an error in the `Build` monad.
-ssystem :: String -> Build ()
+ssystem :: String -> Build (String, String)
 ssystem cmd
- = do	(code, logOut, logErr)	<- systemTeeLog True cmd Log.empty
-
-	when (code /= ExitSuccess)
-	 $ throw $ ErrorSystemCmdFailed cmd code logOut logErr
+ = do	(code, logOut, logErr)    <- systemTeeLog True cmd Log.empty
 
+        when (code /= ExitSuccess)
+         $ throw $ ErrorSystemCmdFailed cmd code logOut logErr
 
--- | Quietly run a system command, returning its exit code.
-qsystem :: String -> Build ExitCode
-qsystem cmd
- = do	(code, _, _)		<- systemTeeLog False cmd Log.empty
-	return code
+	return (Log.toString logOut, Log.toString logErr)
 
 
--- | Quietly run a successful system command.
+-- | Quietly run a successful system command,
+--   returning what it wrote to @stdout@ and @stderr@.
 --   If the exit code is `ExitFailure` then throw an error in the `Build` monad.
-qssystem :: String -> Build ()
-qssystem cmd
- = do	(code, logOut, logErr)	<- systemTeeLog False cmd Log.empty
+ssystemq :: String -> Build (String, String)
+ssystemq cmd
+ = do   (code, logOut, logErr)    <- systemTeeLog False cmd Log.empty
 
-	when (code /= ExitSuccess)
-	 $ throw $ ErrorSystemCmdFailed cmd code logOut logErr
-	
+        when (code /= ExitSuccess)
+         $ throw $ ErrorSystemCmdFailed cmd code logOut logErr
 
+        return (Log.toString logOut, Log.toString logErr)
+
+
 -- | Run a successful system command, returning what it wrote to its @stdout@.
 --   If anything was written to @stderr@ then treat that as failure. 
 --   If it fails due to writing to @stderr@ or returning `ExitFailure`
 --   then throw an error in the `Build` monad.
-ssystemOut :: String -> Build String
-ssystemOut cmd
+sesystem :: String -> Build String
+sesystem cmd
  = do	(code, logOut, logErr)	<- systemTeeLog True cmd Log.empty
 	when (code /= ExitSuccess || (not $ Log.null logErr))
 	 $ throw $ ErrorSystemCmdFailed cmd code logOut logErr
@@ -96,8 +105,8 @@
 --   If anything was written to @stderr@ then treat that as failure. 
 --   If it fails due to writing to @stderr@ or returning `ExitFailure`
 --   then throw an error in the `Build` monad.
-qssystemOut :: String -> Build String
-qssystemOut cmd
+sesystemq :: String -> Build String
+sesystemq cmd
  = do	(code, logOut, logErr)	<- systemTeeLog False cmd Log.empty
 	when (code /= ExitSuccess || (not $ Log.null logErr))
 	 $ throw $ ErrorSystemCmdFailed cmd code logOut logErr
diff --git a/buildbox.cabal b/buildbox.cabal
--- a/buildbox.cabal
+++ b/buildbox.cabal
@@ -1,5 +1,5 @@
 Name:                buildbox
-Version:             2.0.0.1
+Version:             2.1.0.1
 License:             BSD3
 License-file:        LICENSE
 Author:              Ben Lippmeier
@@ -35,6 +35,7 @@
 
   ghc-options:
         -Wall
+        -fno-warn-unused-do-bind
 
   Exposed-modules:
         BuildBox.Build.Benchmark