MacFixIt has photographic documentation of a swollen battery issue. With prolonged use, the battery housing swells and separates, revealing a little gooey residue.
My theory: an owner who touches the battery discovers that it springs apart, and a small alien grabs onto their face, rams its ovipositor down their throat and lays its eggs in their abdomen. Two days later, the built-in iSight camera documents the emergence of the newborn alien via their sternum, and uses Airport Extreme to upload it automatically to YouTube. And thanks to Google AdSense, everyone comes out ahead.
They were saving it as a surprise for 10.5, but I guess the secret’s out now.