I just found this comment on some other site but scary enough to make me think twice before upgrading:
Well I tried vista sp1 and I wasn't really impressed. For one, I lost all (visual)themes (expected) but also lost aero. Not only that half of the shortcuts from the startmenu, and desktop wont work, not to mention to ones in explorer ex Personalize, Control Pannel and System properties. So after a few minutes I decided to system restore back to vista RTmM.