Was happening to me. I started keeping track of the crashed. It was random. Sometimes on Apple apps, sometimes on the main screen, sometimes on 3rd party apps. Happening about 3 times a day. Some people are saying that it was not a reboot, but just the app closing. It is a reboot. Just a short one. (I am hiding apps, and they dont reapear after a on/off start, but they do reapear after a reboot)
I took it to the Apple store on Friday night, They asked me 2 questions then said "Ok, we need to replace this for you" Turns out, it is happening to more than a few. I got a replacement Friday night, and it has only happened once since.