Windows Vista Service Pack 1 (KB937287) issues
Seems Vista SP1 is causing a few headaches, so Microsoft have suspended it's download until they can iron out the issues and get it stable. It's suppose to only be a small percentage of users impacted, so a lot of us wouldn't have become entangled in it. I managed to uninstall SP1 Beta 2 before applying the real deal, SP1;and it all went fine. It was all done in around 45 minutes, and i'm noticing that startup\shutdown is a bit more responsive as well as it being a bit more stable 
Update: Here's a KB article, detailing the currently recognised list of incompatible apps for Vista SP1