The gnomes at XDA-Dev have been busy. Winphoneviet has published an app which allows one to backup application data from apps installed on the phone.
The app requires the WP SDK 7.1 beta 2 installed on your PC, and that the phone be jailbroken.
The software uses ISETool from WP SDK 7.1 SDK to send and receive data to Isolated Storage folder of all apps/games. It does not actually back up the applications, which will need to be installed separately.
Some apps downloaded from Marketplace which are digitally signed may not restore properly, but all side-loaded apps should work with no issue.
Be sure to read the full instructions in this XDA-Dev thread.
WPV App Data Backup can be downloaded from mediafire here.