Windows Networking/Folder Redirection
I had an issue on 02/10/11 where, after moving Personal folders to a new server and changing the Folder Redirection Group Policy, it failed to update the location for some reason. There's a debug log available (see MS Technet) however it was simple enough to fix up in the logon script.
The registry keys for the actual redirection are under HKCU\Software\Microsoft\Windows\CurrentVersion\Explorer\User Shell Folders. Default of REG_EXPAND_SZ type, so you can use expanded variables in the path names such as %USERNAME%.
This shaved off a fair bit of time in configuring/debugging, as I'd already migrated the data over.