Well I had some random reboots on my phone all last week. Some early morning while the phone was charging, some while recording a video, some while watching youtube. Well I brought it to Verizon and the tech said it was a common problem and that it has nothing to do with the hardware, should be fixed with an update soon. Well I did a factory reset like the OP did and for about 3 days had not a single issue. All I had installed was BofA, Clockr, BattStatt, Facebook, Zedge, Dolphin Browser and NESN (a local sports network). Well last night and the night before, I got woken up by a loud DROID a couple times and it was followed by a weird ringing, when I first heard it I looked and nothing so I put it down, but then it happened again and realized the DROID was the phone booting up and the weird ringing was the SD Card connecting.
Well, what I am getting at is that this morning I remember someone on here had mentioned that it was the market updates that were causing the phone to restart. When the phone rebooted on me this morning and woke me up, I noticed that the only notification I had was that market updates were available. If anyone else is getting these updates, try to confirm that this may be the issue and if so, then I will turn it off and see if I get anymore restarts.