The USMT toolkit enable you to capture a user state (profile, settings, files e.g. documents) from a PC during a migration and then restore it onto the user’s new PC. Microsoft has released a new version of this kit.
A great example of how you can use this kit in an automated way is with Operating System Deployment (OSD) in SMS 2003 (via a free feature pack) or with Configuration Manager 2007. You can create a task sequence that includes a step to identify and store the user state on a dedicated file share. The user’s PC can be rebuilt with a new OS build and then the user state is restored. If all goes well, the user won’t be missing any files or data!