How 'warm' is your MacBook operating temperature?
Just as the experience of pain varies from individuals, so is our evaluation of how hot a Mac laptop can become. Apple says they can become "very warm." We can appreciate that warmth in the winter, but it can be a pain for summer computing.
Apple refreshed its Apple Portables: Operating temperature technical note. It says not to worry about "very warm" laptops. There's nothing in the note about "very hot."
The bottom surface and some areas between the keyboard and LCD hinge of your Apple portable computer can become very warm after extended periods of use. This is normal operating behavior.
The bottom of your Apple portable may become very warm during normal use. If the computer is on your lap and gets uncomfortably warm, remove it from your lap and place it on a stable surface.
Duh! Dude, take it off your lap!
My MacBook Pro can get hot at times — more than very warm. Hot.
Sometimes this happens when there's a task that running out of control and overloading a processor. I run a little menubar monitor that shows in real time the load on each core. If I see the little icon going nuts, I can pop open Activity Monitor, check it out and kill the process if necessary.
Jason O'Grady did some interesting temperature comparisons of various MacBooks when he was testing his MacBook Air. Of course, the actual temperature depends on what you're doing, or as in the case of a runaway process, what your MacBook is doing. If you're rendering effects or doing some serious crunching, or you've just plugged your machine into AC power after running on the battery, the bottom of your laptop will get very, very warm. Hot.
In my office, I put my portable on a metal holder that raises the screen off of the desk and lets air circulate underneath it.
When I work in the bedroom (it can happen), I use a wooden tray called the Bed Desk that I bought ages ago at a crafts show. This tray was originally designed to stand books up for reading or as a tabletop in bed. But I've found that by turning it around, lowering the lid and using the adjustable ledge as a backstop, I can work down into the MacBook and the keypad, which I prefer. And this also leaves a gap under part of the case near the fan grids and the left-side power supply that promotes air circulation. A few felt stickers here and there prevents scratching.
Note these warnings from the technote:
Never place anything over the keyboard when operating the computer. Never push objects into the ventilation openings.
I would add: Never let your long-haired cat rest or sleep on the keyboard.