Random shutdowns cured - maybe
I ordered my MacBook (with 80Gig hard drive) a week after they came out and when it arrived I fitted 2GB RAM (from Orca Logic). It worked like a dream (especially with the extra RAM). Then a fortnight after receiving it, having been away for the weekend, it refused to start up again (no bong). Swopped Apple RAM back in but no joy. Phoned Applecare who said they would send a carrier for it. Couple of days later, I tried again and it started but shut down after a couple of minutes. Over next couple of days, rescued important files, one by one. It never ran more more than a couple of minutes and restarted most reliably after a rest.
I sent it back to Applecare and got it back (with new logic board) a fortnight later. Refitted Orca RAM and all is happiness and light - until Mon 28/8/06 when it unexpectedly did a random shutdown in mid-compute (had previously been 14 days since last restart). Had to hold the power button down to get it to switch-off properly and it restarted OK. It hasn't done it again since but it did spur me to do a back-up using Super-Duper. I was worried this might be a sign of things to come, but I reason, computers never fail if you keep backing-up. Its only when there is a risk of losing valuable data that they play tricks.