Reporting something that has happened to me today, not sure if this is a one off or something other have/will experience.
While at work during the day i leave my phone plugged in to a usb socket on my laptop to ensure the charge is kept topped up.
Today at some point I looked down and saw that the screen was off and the notification LED was red. Pushed the power button to wake the screen - nothing, pushed for longer in case the phone had shut down (a friend has had some random reboots) - nothing.. Unplugged the phone, the red notification goes off and stays off when I plug the phone back in, but phone will not boot. The phone is perfectly cool and there is no smell of anything burnt out, so I leave it plugged in for a bit (5 mins or so) and try again, Phone boots but I see I have almost no battery (1-2%). Now, even if the phone had been unplugged I would not expect battery to have dropped so quickly, since battery life has been ok for me so far.
The only possible explanation aside from some OS/Hardware glitch (that I can think of) is that I installed Utter last night, not sure if that could have caused a massive drain in so short a time, but since it is beta I accept it as a possible.