Seems to me that small devices that neither transmit nor receive, such as a pocket digital camera, would be even less likely to cause interference. On youtube, there are plenty of videos in the cockpit itself where someone is actually videotaping the takeoff or landing. Obviously, if the pilots thought this was dangerous, they would never let anybody do this, but it seems like people do it quite often, even in the cockpit itself.

http://www.youtube.com/watch?v=6AM_8QSVEkg