I'd been having some problems with my PowerBook, such as it freezing, and not starting up when I press the power button. I took it to an Apple Store, where the guys at the Genius Bar said it was the logic board. It hasn't been having that many problems lately, but just out of curiosity, I ran the Apple Hardware Test CD, which said there were no problems with the hardware. How thorough is this CD? Does this rule out the logic board as the source of the problem?