I had that happen to a friend who bought a... VisionTek, I think it was? ...4670. The fan gave out on it and he ended up using a box fan until he replaced it with a 9800GT... which then had the same problem.
The 5000 series have the lead in terms of heat on the GTX 200 series. I've been noticing my GTX 260 crawling up to the 80c area lately in gaming... I've been thinking of either getting an aftermarket heatsink (haven't decided which) or upgrading to a new card.
"Don't fix what isn't broken; Just upgrade it."