I had this happen to me while updating to 2.2 in Chicago.. the update (which took a while) wasn't finished when I got in the elevator to the 30th floor of the hotel.. after that, "M" screen of death. Tried pulling battery, nothing worked, would not boot. I'm not a rooter, not extremely technical, but the best I can figure is that the update wiped the old OS, and I lost signal before the new OS was complete. The Droid was dead. Verizon Guy said he'd never seen that before. They sent me a refurbished Droid which I still have with no problems, and now at 2.2. Don't know if it helps but that was my experience.
MD1