This from Harry McCracken on MSN Tech and Gadgets on the disclaimer that graces the bottom of the latest Apple laptops... "Be careful where you put your notebook--it could become too hot to handle."
"Do not leave the bottom of the computer in contact with your lap or any surface of your body for extended periods. Prolonged contact with your body could cause discomfort and potentially a burn." That's Apple's cautionary advice about allowing its notebooks to touch your person, but the problem isn't just a Mac thing. With all the powerful technologies packed inside today's notebooks, the bottoms of many portables get hot, hot, hot. Long-term, using a laptop on your lap could be hazardous to your health--or at least your comfort."
Perhaps we'll see "caution" signs and more disclaimers on the bottoms of laptops such as not to follow the route of the hapless consumer that spills a cup of hot coffee. Or just giant laptop-sized cardboard wrappers similar to the cup insulators I find at my local Tully's Coffee.
When my son found that his computer was warm to the touch on his lap, he used my old lap desk, as recommended in the MSN article. It maintains an air space and enough room between the bottom of the PC and the surface it sits upon: and in the case of a lap, it most likely prevents blocking of much-needed ventilation ports and fan exhausts.