FAA restrictions on electronic devices are caused by the possibility that "some" devices, especially cell phones, "may" transmit on frequencies which interfere with high-priority navigational and guidance traffic, e.g., tower to cockpit. Whether this is so, or not, remains a matter of contention.
The reality, however, is that airlines have the right to restrict when, and at what times, electronic devices may be used. Remember, if ANY device is improperly shielded from electronic interference, whether it's a radio, or not, it can emit signals at indeterminate frequencies.
In theory, nook should emit no more signals than, say, a Nintendo game -- when the wi-fi and cellular radios are turned off. For safety's sake, and to avoid hassles with air crew, I would at least turn the radios off while onboard the aircraft.
