Mine rebooted last night, but luckily for me (kind of) I woke up in the early hours and saw the screen in the boot up loop, so I was able to reset the phone and go back to sleep and wake up with the alarm.
Unfortunately I have experienced this random reboot on all Gingerbread ROM's I've tried. That's Amethyst, Redux, GingerVillian and Oxygen! Perhaps is a Desire/Gingerbread issue?
I might take the plunge back on to Sense and wait for the updated Sense ROM when HTC release it...