I had been using my GTX 260 since late October 2011 to mine up until a few months ago. I now use it to mine litecoins instead. Temps have hit as high as 96C sometimes, but averaging mid to high 80s usually. And it's still running like a fucking champ. I'm honestly just waiting for it to die so I can get a new one, but so far it hasn't yet.
And yes, 96 celsius, not fahrenheit.