You can download a user's guide from here:
http://www.google.com/url?sa=t&sourc...jV9dwnVADfXLzg
From the User's Guide:
Wireless Safety
In general, turn the wireless switch on your Kindle to the OFF position in areas where its use is forbidden or when it may cause interference or danger. Some specific situations are described below.
In general, any place you are not allowed to use your cell phone, you should not use your Kindle with the wireless service turned on.
Turn Off Wireless When Flying
Turn off your wireless service before boarding any aircraft. To prevent possible interference with aircraft systems, the U.S. Federal Aviation Administration (FAA) regulations require you to have permission from a crew member to use your device’s wireless service while the plane is on the
ground.
If you have your wireless service turned off, you can use your Kindle for reading once a crew member has said it is okay to use approved electronic devices. [Emphasis is mine]
Looks like use during takeoff and landing would be a NO.
But you will probably get some responses here that such rules do not apply to FlyerTalk members.