We’ve been implementing a large TFS 2010 installation and recently started the migration from VSS. I’m writing to say that so far I’m impressed with the migration tool. It’s clearly documented in the MSDN library. A couple of XML configuration files drive the app. After setting up the config files you launch the migration process from the command line. I was surprised to find that you can migrate any subset of projects from VSS at a time. You don’t have to migrate the whole VSS database in one shot. I was also surprised to see that the tool mapped VSS users to TFS users and preserved version history by users. Remember to create the target users in TFS, then edit the user map file to point VSS users to TFS users.
It all works great so far. Now keep in mind we’ve only done a small pilot project. I’ll write back once we get onto larger ones.