My framerate in games dropped by more than half after installing sp1 via windows update. Hardware/process monitoring revealed nothing out of the ordinary.
I did have this problem before with the version from technet. After weighing my options I opted to reformat and start again with a clean install. That fixed the problem in the past. This time a reformat made no difference.
This certainly wasn't what I expected.
Well, to all you guys going off on that one guy for saying his benchmarks fell: boom, here we got a real problem now!