Mopar has the right idea
I'm an electrical engineer, maybe i can expain the 'issue' with electronic devices.
From an electronic point of view:
Basically, whenever electricity flows, it creates a field. Think electromagnets you made in 5th grade - wrap a wire around an iron nail, attach a battery, and the nail is magnetic.
Whenever there's an electric field, it causes electricity to flow in anything that conducts. Think holding a static-charged towel close to a florecent bulb - the bulb will light up.
This means that any time you use anything electronic, it creates a field that can interfere with other electronics. with most portable devices, this is miniscule, but it does still exist. This doesn't mean the other device will fail, but it could get messed up - think about putting speakers too close to your TV.
Now, from an engineering point of view:
Boeing, Airbus, and everyone else have to design the computer systems in their airplanes. Because it's a critical system that means life or death, they have to test it very carefully and extensively. Under normal conditions, lets say an airplane will be fine 99.999% of the time. If a GPS running anywhere in the plane changes that to 99.998%, then that's grounds enough to not allow them. Chances are, though, they don't bother testing the case where a passenger has a gps and so they simply say they shouldn't be used - meaning they can't guarantee 99.999% sucess because they haven't tested.
The bottom line is that electronics could cause a problem but the odds of it happening are so slim it's truly not worth considering.
-Joe
"Can't spell geek without EE"
