DARKFiB3R, on 05 January 2013 - 01:57, said:
This one I repaired a while ago...
This was a particularly bad case, due to the owner being a smoker, so the dust was all gunked-up with tar. Usually, a vacuum cleaner would be enough, but in this case, I had to give it a proper clean out with isopropyl alcohol.
But even without being a smoker, you can often still get a thick layer of dust over the heatsink fins, as shown above. It actually peels off like a felt pad

Ahhh dude that must have smelled awful!