While most users have been unaffected by the upgrade to WSUS SP1, there are a number of scenarios where problems may occur. Microsoft just released an updated WSUS SP1 Readme file that details all current known issues. I’ve seen a couple of these first hand, and helped others with them via the WSUS public newsgroup. I even had a guy approach me at Tech-Ed with a failed upgrade (he renamed his server after installing WSUS, but before upgrading to SP1).
Even though WSUS SP1 is a ‘true’ service pack (meaning no new features) it’s still wise to look before you leap. If you find any additional issues with WSUS SP1, please post them to the public newsgroup ‘microsoft.public.windows.server.update_services’ and the product team and MVPs will do our best to help.