I just ran across this really disturbing article on Hack-a-Day.com (great site) about listening to the rf interference generated by keyboards as far away as 20 meters, even through walls.

Tin-foil hat time....

Compromising Electromagnetic Emanations of Keyboards Experiment 1/2 from Martin Vuagnoux on Vimeo.

Compromising Electromagnetic Emanations of Keyboards Experiment 2/2 from Martin Vuagnoux on Vimeo.