I have heard some people talking about the heat issues on the "older" powerbooks, this must be what they were referring to.
It appears that they "fixed" the problem on the 1.33, and 1.5 ghz models to some degree. (no pun intended...) my 1.5 (15") never heats up to the point the it's a concern.
If it's to the point that it's unusable, you have no choice really other than to consider a trade in, or an upgrade.