Yesterday my PlayBook get stuck. I was able to pop up some dialogs (for a while), but no touch response, hence no way to actually reboot it. I did some search on various forums, but found only way to hard reset it (a.k.a factory reset).
After a while of playing with buttons I found a way. Simply press and hold power button for 5+ seconds. This will turn off you PlayBook (I wasn’t able to see this because of the screen being frozen). Wait a while so the device can do all the shutdown stuff (the screen blanks). Now press the power button again and PlayBook will begin booting.
If you know other ways, be comments for you.