The only solution I found was to reset Windows Mobile.
ITWire received emails from users who experienced problems after installing SP1.
One is that the memory and performance rating is not displayed anymore, and the other one is about the Windows Mobile Device Center.
This article (KB935796) lists all known programs that don't work properly with Vista SP1.
I suggest you check them out before you install this service pack.
This issue was the reason why Microsoft postponed the general release of SP1 to mid-march.