I watched many sci-fi movies where guys were playing around on the keyboard and trying to hack someones system by figuring out password etc. You already know that every individual has his/her own way/speed of typing on the keyboard. Biopassword has made a product on such grounds. There product captures the keystrokes and builds a pattern in which user key in the password etc. During authentication there software checks for that pattern and denies the access if the pattern does not match. I have tested the demo on there site.
You check it out by yourself and have fun.