So I had my iPad 2 on my desk while working on my iMac. It was not doing anything, no apps were running, it was just sitting there on the home screen. In fact, the screen was off. Then with the corner of my eye I saw the screen light up and the apple logo appeared. After a minute or two it presented me with the passcode screen. I entered it and everything was fine. Any idea of what is going on here? Again, the iPad was "off" and not running any apps (at least not actively) and it appears to have spontaneously rebooted. Had it not been in my field of vision I may not even noticed it happened. Also, the battery is at around 50% so it's not due to that. I just hope nothing is wrong with it!