I've had these problems for quite a while now, but I'm finally posting about this because I can't stand it anymore.
I have an EVGA 8800GTX.
This seems to be an off and on sort of thing, though as I sometimes don't play a whole lot of games the problem may not be intermittent at all.
I don't know the correct term for this. Basically, once in a while, I'll be playing a game, and everything will freeze up, then, all the textures on everything changes and turns to slo-mo where i'm lucky to get a single frame every 5 seconds.
I took this screenshot a while ago with warhammer:aor:
As far as I can recall, the sound always continues to play in the background, and usually, if I wait long enough, I can alt tab out to task manager.
The last games I can remember having this problem in have been Warhammer:aor, Age of Conan, the Call of Duty 5 WaW beta, and just a few minutes ago, Fallout 3, though there have been others in the past.
I'd love for someone to tell me what's going on :]