Me Too...
I'd been having some problems with my PowerBook as well, none that make the computer unusable, however. Sometimes the computer won't start up on the first time that I press the power button, and occasionally it'll freeze on me. I took it to a few people who told me it's most likely the logic board.
From what I've been seeing, these boards sell for approximately $550, and the installation doesn't look too painful if you follow the link from Reflow.
However, if you don't have any physical damage to your computer like dents or anything, take your computer to an Apple Store, and I think you can send it in for about $350, including shipping there and back, parts, and labor.