Hmm... Odd... I wonder what exactly this could be, I just experienced my first random reboot. It reminded me a lot of an Android low voltage reboot (custom ROMs) where a custom kernel is flashed to allow the CPU to function more "efficiently" by up clocking the CPU and keeping its voltage low which in turn uses less battery for its performed clock speed, however, there are times when things get too processor intensive too quickly and because the kernel is giving less power than usual, the processor sort of "short circuits" if you will, and the phone ends up rebooting. I'm not sure if that's what this is exactly, but given that performance has improved with the recent firmware update, HTC probably increased the clock speed and I may have experienced the "short circuit" that I just explained... Hmm... Who knows, I'm sure it'll be gone with mango though.