I was discussing this topic with Bu Yousef a few weeks ago. This is a copy/paste version of my response to him (yes I'm lazy!). Just a quick solution to those who are experiencing overheating issues with their Mac.
"It's normal for a MacBook Pro to overheat from time to time when it's multi-processing but not to alarming levels as cooling all the time - cooling fans reach over 6000rpm - screen starts to flick.
Which version/update of OS X do you have installed? If it's 10.5.6 then it's known for causing fatal overheating issues thus you'll need to either update for the most recent version or reinstall OS X (not format just reinstall it so it can overwrite the system files back to normal). However, make that (reinstallation of OS X) your last resort if nothing works.
First things first...
- Room temperature: If it's not cold the macbook pro will heat up fast so make sure you operate in a cool environment.
- Operating surface: Put the macbook pro on a flat solid surface, neither on your lab nor on sofa, carpet... etc. to keep it ventilated.
- Charging: If your macbook pro is charging it is more likely to overheat while processing but once the charge is full it should get back to normal unless there are severe processes (video editing, multi-browsing with lots of Flash activity, ..etc.)
- Download iStat Pro on your dashboard: See if the fan speed reach over 6000rpm or CPU temperature goes over 70~80c, if it does then it's not normal so you can carry on with the next step...
- Go to Finder > Applications > Utilities > Disk Utility and choose your Macintosh HD. Click "Verify Disk Permissions", it will take some time then when it finishes click "Repair Disk Permissions".
- Open Activity Monitor when the macbook is overheating: Look for the process that is taking a lot of CPU usage and quit it then try resetting PRAM & NVRAM.
That's about all you can do to resolve the issue. If nothing helps then as I pointed out earlier in this email try updating with the recent OS X version or reinstalling OS X from the CD. Reinstall only if the overheating is severe (reaching over 6000rpm and CPU temp reach closer to 100c on iStat Pro)."