The Apple Blog has an interesting story on why Macbook Pros Are Hot:
Over at the Something Aweful forums, a user has pointed out that one of the reasons the Macbook Pro gets so hot is because of a misapplication of thermal grease. Now you can read the full article with pictures, or the instructions to disassemble your Macbook Pro yourself; but it does appear to have taken the temperature from about 55 degrees down to 39 degrees. This may void your warranty, so take extreme caution in attempting to do this, you do not want to destroy a $2500 computer.
I won’t be trying this myself: so far, I’ve found my MacBook to be pretty cool-running. The only exception to this is when the DVD drive is running, when the heat – and the noise – crank up quite a lot.