I fly a bit for work and play. Of all the regulations that require compliance the worst are the limitations on the use of electronics “during takeoff and landing.” When you’re flying in and out of large markets the “takeoff and landing” portion of the flight can be an hour or more.
Nick Bolton does a good job asking the question on his New York Times blog but comes up empty.
According to the post, the FAA requires airplanes be able to withstand 100 v/m (volts per meter).
From the blog post:
When EMT Labs put an Amazon Kindle through a number of tests, the company consistently found that this e-reader emitted less than 30 microvolts per meter when in use. That’s only 0.00003 of a volt.
OK. But the post goes on to ask the obvious next question: LOTS of people have Kindles and iPads. What about THAT!?
But one Kindle isn’t sending out a lot of electrical emissions. But surely a plane’s cabin with dozens or even hundreds will? That’s what both the F.A.A. and American Airlines asserted when I asked why pilots in the cockpit could use iPads, but the people back in coach could not. Yet that’s not right either.
“Electromagnetic energy doesn’t add up like that. Five Kindles will not put off five times the energy that one Kindle would,” explained Kevin Bothmann, EMT Labs testing manager. “If it added up like that, people wouldn’t be able to go into offices, where there are dozens of computers, without wearing protective gear.”
Technology & Patterns 
No one really turns “off” their electronic devices. On any given flight, there are several dozen electronic devices still in a “powered on” state in the passenger compartment. Some group somewhere just wants travelers to be as distraction-free as can be possibly mandated to hear the ‘how to unbuckle a seatbelt and get to the closest exit’ speech so that flight attendants can keep a bit of job security. No one listens to those speeches either.