Well, I shouldn't have said I was one of the lucky ones. I was 55 minutes into a 1 hour carve, and my CompuCarve spontaneously stopped with the bit still plunged into the wood.
The LCD was completely blank, and adjusting contrast to extremes didn't change the display, so there seems to be no power at all. I checked the wall socket, and it's good, but switched it over just for good measure. Still nothing. I checked that I could still read the card on my computer, and it looked good, but I re-flashed the firmware anyway. Still nothing.
I'm almost at day 90, so I think I'll just exchange it back to Sears unless an answer just pops up, since it seems like it might be the fastest way to get another one to keep making sawdust. Besides, if I keep getting one every 90 days, I can keep my unit under warranty forever!