I too was on this flight and noticed this when I went to the Lav.
People just want to see where they are. It is against FAA rules to use GPS devices in flight. But does that stop people? NO.
A gentle person was using there telephone on this flight too. Two other phones rang during the flight also. The only reason I know this is because I was trying to sleep.
The man put the PDA down because he does not want to turn it off and probably just wants to see his home or the area he lives in from the sky.
Look - Not many people turn there electronic equipment off during short flights.
Not everyone is a terrorist.