FYI: Reported on MacFixIt and Slashdot...

It appears that some batteries in Mactel MacBooks are getting hot and swelling up enough to disrupt the circuitry and pull the casing apart. Apple is replacing them on a per-request basis. This is not even close to the debacle of the infamous Mac "fireball" 5300 laptops but could still cause some serious damage. Check your batteries!

P.S. Slashdot also has a link to photos of an old Dell laptop in flames at a conference. The owner never bothered to get the free replacement battery.