Had an embarrassing moment with GPS on a flight a few years ago when I started my iPhone GPS based "Speedo" app "just for fun". It took a while to get a fix but when it did started to sound it's quite strident alarm! I'd forgotten that I had it's speed warning set to 80kph. We were doing over 800!
I didn't know GPS wasn't permitted during flight. I also assumed it was passive.
I have a very neat set of photos taken with an iPhone through the window of an A380 over Turkey which are all neatly tagged with their location. Pity not to be able to use that functionality.