I was on American Airlines recently on a trip that put me on 4 different AA planes. I periodically checked GPS on my iQue M5, which is also my PDA and MP3 player. On the last flight, a flight attendant spotted me and asked what it was. "A GPS" I told her. She said, "You'll have to turn it off." I replied, this one only receives - It cannot transmit anything." The logic of this was of no interest to her. She stated that GPS's are listed in the Inflight Magazine as banned on flights. Of course, I promptly apologized and let her know I would turn it off. In retrospect (and trying to find some logic in it), I suppose that there is a slight terrorist rocket attack risk that could be supported with GPS coordinates, but I don't have a good understanding of such things.