When the phone is shutting (on battery out), its not unmounting the filesystem properly, and someway ends up corrupting the filesystem. On bootup, sometimes it recovers from the error by filesystem checks (?), and sometimes it fails completely (and you get a lemon).
I've noticed that if you shutdown the phone (and not drain it out), it always boots up (maybe I'm just lucky).
Google should atleast keep up posted if they have a fix being readied. Google/Paul, is it too much to ask??