This relates to my Late 2011 MBP AntiGlare 2.2Ghz If I set relatively dark solid desktop background, load my MBP to heat it up (like handbrake converting full-length HD movie), and make fans run at 6200 rpm, here is what I see on my screen: Both dark areas are right next to fan exausts, so I suppose, that is heat issue. It appears quite quickly - takes ~2 mins. And then disappears same way once job is done and it is cool again. In real life it looks way less pronounced, than on this picture and I can live with that during high loads. But I need to make sure that is not going to be a permanent effect over time.