This is the reason why I thought Apple was foolish to go with an NVIDIA chipset--NVIDIA's QC is absolute crap and they seem to have no ability to improve it. Having said that, I have a penryn MBP ('early 2008') 2.6GHz with the 512MB G8600 and it is still fine. I run the fans at 3500 RPM continuously, hoping to ensure that things stay cool enough to avoid spontaneously burning out the GPU.