I've noticed that my MacBook is running very hot recently and being a Intel Core2Duo machine, the hotter it is the slower it runs. It's slowed to such a level that even watching video online is a problem.
So, finally this week, I opened up my MacBook and blow the dust out of the fan and the heatsink. After the dust is clear, the computer is much cooler, from 45 degree to 37 degree idle. Pretty good!
Also, I snapped some photo when I was working on the computer, here is the inside of the MacBook.