Our CSci department chair, Dr.Walter Read, was interviewed on local TV news about whether someone can "listen" to you keyboard and figure out what you are typing.
Here is a link to the story and video:
http://www.cbs47.tv/consumeralert/story.aspx?content_id=15FA3F41-9002-4079-9E0F-A8D8E8572A18
The academic paper that started this discussion is:
http://www.cs.berkeley.edu/~tygar/papers/Keyboard_Acoustic_Emanations_Revisited/preprint.pdf