Hi my graphic card cooking lasts since a month now and works perfectly, I'm using istats menus as temperature monitor and the heat stays between 40 and 75° Celsius when I watch movies.
I have an imac 20" 2008 which had no problem but I monitor it also and when the temperature of the AC/DC supply goes near 80°C I increase the fan speed to make it work under 70°.
Curiously the 24" doesn't heat as much as the 20".
The idea I think is to keep the AC/DC supply and the CPU die under 70° C by increasing the fans speed.
I'll post if the graphic card needs another baking, but in the meantime I cross my fingers !!!
André
PS : the mbp 2007 doesn't support temperatures much higher than 82-85°, it shuts down by itself, I imagine that Apple provided the same precaution for the imacs but it never happened to me.