Apple KB Article: How to Warp Your ALPowerbook Faster Than You Can Fry an Egg

Okay, so that's not really the name of the Knowledge Base article in question, but I just noticed
How to use your PowerBook G4 with the display closed
and it made me immediately think of the heat issues involved.  Two out of the 3 12-inch PowerBooks I've owned have had slight warping issues due to heat (and this is a major design flaw, imho, which Apple should address). Actually, I
guess I've had 4, as the FIRST one I bought came prewarped and was traded off within a week.  In any case, these machines put off a lot of heat, and I am expecting my current PowerBook to eventually start to wobble from the hours and hours I spend typing away at it. As most of the heat builds up just above the hard drive, which is located under the space on the left side of the trackpad, I can't imagine operating with the lid closed. This would effectively decrease the heat dissipation and increase the warping of the aluminum.  Do any of you PowerBookers work this way?
Have you noticed heat or warping issues as a result?