On Windows Vista or later, the whole %appdata%\Bitcoin directory can be replaced with a symbolic directory link:
(0) Make sure the bitcoin client is not running.
(1) Move the %appdata%\Bitcoin directory to its target location (e.g. d:\bitcoinData)
(2) Run the command prompt as root and issue the command mklink /d "c:\users\\appdata\roaming\bitcoin" "d:\bitcoinData"
done!
This allows you to keep bitcoin client data anywhere, e.g. on a secure local fileserver.
Guys, Really this is the better one, I literally forgot that i was using it, ive been using it all the bitcoin clients across my house's computers it works great and im even using Shortcuts instead!