My 2nd Gen NTSC Fat 80GB crashes roughly once a week; only from usage in online lobbies or accessing online features. During offline gameplay, it has never crashed or had any issues. No overheating, no artifacting, or pixel/framerate issues. I've had Indy road course(online) have multicolored track texture issues, but returning to the pit fixed the issues - the back straightaway looked like rainbow road. Others reporting this has made me believe its a bug in the game, and not PS3-related.
I have had such a severe crash, however, that corrupted my HDD and made me do a complete wipe. It's a WD 500GB laptop drive, which I don't think was the problem as much as the game writing to the disk during the crash.