Interesting. I posted a message on this very subject on the Passengers / SLF board back in April this year. I've been trying to find a way to post a link to the thread, but haven't succeeded - if you want to look at it, just do a search on "Use of hand-held GPS" on the Passengers / SLF board.
Anyway, in essence, what I said was that I regularly used to carry a small hand held GPS unit on commercial flights. It was a simple Magellan Sport Trak unit, which had a very rudimentary moving map.
For it to work, it was necessary to hold it quote close to a cabin window to enable it to "see" the satellites, as it had no external antenna, and no provision for attaching one.
It was then possible to monitor our position, ground speed, heading, and if our destination (or somewhere close to it) was in the internal database, it would also calculate our ETA.
As a PPL (A) this was all interesting stuff, and also answered the inevitable "where are we" questions from my travelling companions.
On one occasion, a member of cabin crew spotted it and asked what it was. I explained that it was a GPS receiver, and as the lady's husband was a PPL also, she was familiar with the device, and quite happy for me to use it on board.
However, on another occasion, we were coming back from Spain on an ****jet flight, and a member of cabin crew spotted it and asked what it was. Again, I explained that it was a GPS receiver. She then told me (in no uncertain terms) to switch it off immediately, and that devices like that were strictly prohibited on board.
Replies to my posting on the other bulletin board varied from the highly technical (most agreed that whilst in essence, as it was a receiver, it could not interfere with the aircraft systems) to the downright insulting, where I was accused of being an anorak and likened to spotters.
However, it is most interesting to get a definitive answer from None's Op's Manual.
Regards
OM