A new script has been added to the standard client task sequence template in Deployment 4 Beta 3. This script helps with the USMT data migration process by scanning the existing OS to see what file types are registered to applications installed on the machine, then generates a new USMT XML file to tell USMT to grab all files of those types. While this doesn't do anything to help with the migration of settings associated with those applications, it at least does make sure that data files are captured and restored.
Check out the ZTIAppXmlGen.wsf script to see how this works. Right now, this will only work for Lite Touch and SMS 2003 deployments.