I have the same problems like in the 2nd post. I also get them, when i use Eclipse oder iTunes. So it doesn't depends on the application you use in the moment.

I think it is a OS problem. My temperatures are at a normal level when the artifacts appear. I hope 10.7.3. will fix it. The issues also disappears when i refresh the website for example.

I look forward to a fix. It didn't happend when i used Snow Leopard...