I sortof agree with beee, my keyboard makes pretty loud noises when pressing and releasing keys, and it makes a fairly loud click when i rest my finger back on a key I just got done hitting, and sometimes ill type two or three letters before letting go of the first key I hit. I'm wondering if the test recording they used might have been someone deliberately typing somewhat slowly, or if they tested it on different types of keyboards. Laptop keyboards would probably be most susceptible to something like that I think.
Either way it's a scary thought. I'd love to just look at the algorithms they use for something like that.

Thx for the links guys, I was searching for accoustic keylogging and the like