I have my MacBook Pro sitting on my desk and it's consistently over 160 degrees. It is almost too hot to touch in some places on the casing.
160 degrees Fahrenheit, if it is CPU temperature, is normal for MBP.
MBPs are designed to run pretty hot, with the aluminum case as the main heatsink the casing gets uncomfortably hot sometimes.
If you want to remedy the problem:
- use a laptop stand (I use Belkin Cushtops, they are really comfortable),
- put your laptop on steady, heat-transducing surface (human skin, blankets or soft chairs are bad — wooden/plastic/metallic tables are good),
- open up the casing and clean the dust (can make it ~10 degrees Celcius cooler)
- or, use less video- or CPU-intensive application =)
If you're interested, I've had a lot of luck manually regulating my MBP's temperature a little better with smcfancontrol. I find that keeping the fans running at 3,000 RPM by default (instead of the normal 1,000) adds no ambient noise over what's already in my office and keeps the temperature a bit lower. I also use it to pre-emptively turn the fans up to 6,000 RPM when I know I'm about to do something that will make it run hot.
Short answer: because of the crappy nVidia chip in it. See here for more details and don't forget to use some sort of app to see your actual temperature details. You'll see it's the GPU diode that's burning up. The rest should be hunky dory, at least 12 degrees centigrade below that piece of... extraordinary nVidia technology which I will forever remember for this snafu.
Long answer: I currently have one of those pre-Unibody 17" MBPs, with the faulty nVidias. Oh yeah, I'm so happy, I can hardly hold it in.
It initially ran at about 75 degrees Centigrade when I used it. After putting it on a smcfancontrol diet and keeping the fans revved up to 4500 as a default, everything was hunky dory except it still ran at about 69 degrees and was burning my forearms (though I love it in the winter).
Long story short: bought a wireless keyboard, turned the fans down to their standard 2000, 4 weeks later I'm the proud owner of an MBP with a dead nVidia chip on it. Luckily, I had Apple Care so everything was fixed literally without any questions. The new logic board had the gpu diode running at 63 degrees for the first two weeks (with fans turned down). Now their default has become 72 degrees with the fans at 4000. I think I'm going to turn smcfancontrol off, make the default 2000 again and let it burn.
I wonder how many dead nVidias I have to get in so that Apple replaces my notebook with a version that doesn't have a crappy nVidia card in it.