I have two 7600GT cards in SLI, and I get corrupted graphics in more demanding games (like Bioshock, Stalker, Timeshift) after running them for a few minutes (I use 1280x1024 and get decent frame rates by the way). This doesn't happen in older and "lighter" games like Painkiller and HL2, except very rarely and to a much lesser extent, and only after running them for a long time.
I monitored the temperatures while playing and they do get pretty high, although I'm not sure if they're abnormally high. Last time I checked they got to 71°C and 70°C for each card respectively. Could this be the cause of the problem? I opened the case recently and the fans were pretty clogged with dust, and while I did do a superficial cleaning, it didn't make any difference. I'm thinking of disassembling the whole thing and give the fans a proper cleaning, but I need to make sure that this is a temperature issue before I can overcome my laziness and commit to doing it. Frankly 70°C doesn't seem THAT high to me. Is it?
The garbled graphics could be because of some memory chip on the card overheating. They are probably not equal in terms of air flow, so increasing fan speed might not help. 70 isn't that bad under load but if you're starting to hit 80, I'd do something about it.