I've regularly used my GPS on board for several years. I also regularly connect it to my laptop and run StreetAtlas. It's really cool to look out the window and say "Hmmm... SR50 and SR6, East Ely, NV." On most planes, I can "stick" my external antenna between the window and the shade. Sometimes I get a solid lock right away. Other times it takes 30-45 minutes, and then only for an intermittant fix.

I used to always ask the crew if I could use it, but it just got the point where the answer was always "yeah, sure." The best response, after the FA asked the captain, was "Sure, and if you could figure out where we are, please let us know."