I often worry about my GPU temps. I have a Nvidia GTX 470 and while playing FFXIV it constantly runs around 80-90c, sometimes peaking above 90c.

But I haven't had any shutdowns or anything.

I've played for a few hours on many occasions with GPU temps around 90c. So far It doesn't seem to have any problems.
(This is on two screens btw, one for game an other for internet. Changing from one screen to two increases the GPU temp quite a bit).