I'll add my experience to the above random MacBook Pro shutdown issue. First let me say that I've LOVED Apple for the past 20 years, and this faith is unshaken by this annoying glitch which I'm sure they are as eager to remedy as we all are.
I upgraded my old PowerBook G4 to a loaded MacBook Pro with 2gigs of Apple RAM in 8/06, and I'm delighted with it (fast, FAST) except that the screen occasionally goes black and freezes.
BUT here's some additional info for everyone: I have external Mac monitors both at home and at work; and these, while frozen, continue to display whatever was on them when the main laptop screen went black. The cursor still moves in response to the touchpad or USB TurboBall, but clicking anywhere on the external screen does nothing. The only way out has been to hold down the Power button and restart.
BTW, the sudden blackout has also occurred when I was using the laptop without the external monitor; so without that monitor it looked like a shutdown when it was actually a freeze - two entirely different phenomena.
I've call Apple support several times, and this is what we've tried so far:
1. First we checked all the Sleep settings (which were fine)
2. Then we reset the PROM.
The next day the blackout recurred; so I called AppleCare again. (I ought to mention that everone I've spoken to there had been GREAT and eager to help).
3. The next thing we tried was resetting the PMU (Power Management Unit)
The blackout problem recurred several times over the next few days. The blackouts have nothing to do with computer activity or inactivity - they have occurred while typing in a Word document, rendering a long video with Final Cut, or even when the MacPro is sitting all by itself doing nothing (I come back to find the main screen black and the external monitor frozen except for the cursor)
4. AppleCare then had me reinstall the whole System from the DVD which I did yesterday (THAT took half a day to get all the updates and get all programs up and running right again), but the effort was obviously necessary to rule out a software glitch.
I've got my fingers crossed that this will do it; but if not, I'm absolutely certain that Apple will treat me right. As I said, I'm a devoted Mac man to the bone.