Every story I've read has either had an incident while the Phone charging. Any reports of incidents while the device was simply being used? Or even more unlikely, powered down?

Note that the the FAA is just encouraging you to (1) Not check them in luggage (where nobody can put a fire out easily), (2) Not charge them, (3) Use them inflight.

I haven't seen any problems with the phone in a powered down state - anybody else?