I have my two ATI 6790's running between 75 - 85 C. I had read on a number of sites that anything less than 100 C won't damage your card, but I was still concerned, so I contacted my card manufacturer (HIS), and they said that even as high as 100 C should be fine. I suspect that they weren't considering continual use like in mining, so my new *play it safe* cutoff is 90 C, but I don't even see how I would get that high without overclocking.

The CPU temp should be considerably lower. The sources I was able to find on the internet recommended keeping the CPU and motherboard temps below 70 C.