That electronic devices might pose a threat to commercial aircraft through electromagnetic interference has already been discussed many times (for example here).
What I'm concerned about is the possibility of executing a terrorist activity through a nefariously modified electronic gadget. An iPod touch or a MacBook could be modified by adding high-power radio transmitters, and could be used to reliably cause interference with an aircraft's communication and navigation systems. Such a modified device would easily pass the security checks at airports, since it would look and work just like any other iPod touch or MacBook.
I'm not sure if anyone has ever thought about the possibility of what I've written above. Most of the published material appears to be concerned about electromagnetic interference from electronic gadgets used by travelers (and travelers either forget to turn their devices off or they deliberately don't turn them off - we all know this).
However, I can predict that in the near future, devices will begin to automatically recognize their current location and take at least some safety-related actions based on their location. For example, smartphones or tablets of tomorrow will realize that they're inside an aircraft or a hospital and will either alert their owners of the possibility of interference or will automatically turn off their wireless components. Alternatively, a transmitter in an aircraft's cockpit will send a signal (at the order of a pilot) ordering all electronic devices to turn themselves off. Compliant devices will either alert their owners or will automatically turn themselves off.