I have a MacBook Air bought in early 2011. Lately it just can't seem to stay cool. With normal load, the CPU hovers between 80ºC and 100ºC, and if I use iStat / Fan Control to turn the fans up to full, completely idle my laptop will still only cool to 75ºC.
I've opened it up and taken a look, and there isn't an obscene amount of dust in there, though I did give it a good vacuum and dusted it with compressed air. In particular, the part of the heat sink where the fan blows through seemed a little clogged, but I took to it with a vacuum cleaner. This hasn't had any noticeable improvement.
I'm wondering if I need to look into the heatsink, since the fan seems to run correctly (there was some dust caked onto the fan blades, but nothing that stopped it spinning).
Here's a screenshot I took of iStat: