Phone keeps turning off and on ?

Have you tried a factory reset without restoring any backup?  Does the device feel warm or hot to the touch?  I haven't seen anything on the Samsung Members boards that would make me think there is an issue affecting a lot of people.  If a factory reset without restoring anything doesn't resolve it.  You might want to send it in to Samsung for service.  If you are confident in flashing your device.  Doing a complete full flash with ODIN is one more step to eliminate it being a hardware issue but only consider that if you understand and are confident in doing so.  Flashing can brick your device and leave it in a non-bootable state if not done right.