Hey fellas!
When I was investigating my performance problems I thought it was my GPU having a full VRAM - because iStat Menu showed this (first only occasionally now all the time - even after rebooting). So I came across this forum thread where somebody is stating that this might not just be an iStat Menu displaying error but more of a general problem in 10.8 which in fact IS affects the performance of the machine.
This is the forum thread: http://forums.macrumors.com/showthread.php?t=1416468 (post #13).
Sooo... anyone else experiencing performance issues? iStat bug? 10.8 bug?