Check with your airline to see if they allow GPS or not. Delta for example clearly states

You can use these while the plane is at the gate with the doors open, after the plane has taken off and reached its cruising altitude and before it begins to descend for landing, and after the plane has landed and is taxiing to the gate.
Personal digital assistants
Personal computer games
GPS (global positioning satellite) systems

There is a short piece in the NY Times this morning with a bunch of links to companies that offer solutions to geotag photos

http://www.nytimes.com/2009/03/05/te...5askk-001.html