Interesting authentication mechanism

Interesting article on identifying a user based on their typing patterns.
http://www.physorg.com/news67710818.html

Some questions I had after reading this:
1. how does the server detect replay of captured keystrokes i.e. of my name (perhaps you're asked to key in a one-time challenge)
2. what if your style of typing changes e.g. I see a google ad right next to it which says: Improve Your Typing Skills. Get Better Speed & Accuracy. Act Now
It would be interesting to find out more on how this works.