Yesterday the chaps at The Tech Report reported on an issue affecting a good chunk of GeForce 8800 users, where 3D graphics performance would fall into the toilet at random and wouldn't come back until you restarted the game or tabbed out and back in. NVIDIA got back to them and said it was a driver issue and that the driver team were working on a fix. Oh well.

Now Beyond3D reports that the slowdown bug is probably caused by texture eviction from device memory. Textures aren't being evicted when they should be, causing a loss of available device memory for other resources. So it stands to reason that if you restart the app or tab out and back in, both of which reset the device which causes a VRAM flush, you'll be good to go again. It's somewhat application dependent and depends on how the app does surface management, but a general fix should be possible for all but the most misbehaved programs. Let's hope they fix it as soon as possible.