It seems to happen more when I’m holding the laptop or moving it around, which would lead me to think that it could be flexing and dislodging something lose. It happened once today while I was at work and it was on my desk, but my home office is so cold I wouldn’t rule out thermal flexing. It failed tonight while I was standing there holding it in the Apple Store waiting for it to finish booting, it failed again while I was carrying it to the dinner table, and it failed just now when I picked up my computer from the floor.
It happened when I was logged on as Guest, which was something the Apple Store Genius suggested I try.
Whenever I reboot it because of this, Spotlight is busy indexing and can’t be used for a few minutes after it comes up. This is slightly annoying, because I use Spotlight more than the Dock to start up programs. But more than annoying, it’s worrisome because I don’t remember that happening before.
Tomorrow I’m going to try booting it from the install disk and seeing if it fails while it’s running off the DVD.