Some time back I reported on crashing the Macs here using a non-trivial GLSL shader program. This bug still exists to this day. Now we’ve got a small, brand new 21″ iMac, fresh out of the box. It exhibits a similar problem. This time, the UI does not lock up, but the rendering is totally borked. Compare the two screenshots. The first one shows the correct rendering, on a Linux PC using an NVIDIA GTX285 GPU, the other one is from the 21″ iMac using an ATI GPU. The trick between crashing and not crashing seems to be the ATI brand…
didn't it work well on my nvidia MB gpu?
Yes, you said so. But your machine was the very only one that worked. The machines at the i4 fail as well. Anyway, I have updated my Apple bugreport. Let's see if they report anything back… Haven't heard from them in a while, report is still open.