And I bet 99% of them will be "Shave and a haircut...2 bits" ;-)
I was at a MS security summit back in 2004 where steve ballmer presented a product/company similar functionality. I believe it was called "biorythym" but dont quote me. The general idea was to recognize the users password in addition to the "rhythm" the password was typed.
This was 2004 and it looked cool, but I never heard any mention about the company after the convention.