ibi research at the German University of Regensburg has developed a keyboard typing behavior based psychometrical authentication method.

The PSYLock method uses the fact that each computer user has an individual typing behavior. Apparently the typing behavior is a significant and personally individual feature, which cannot be copied.
I am sure that everybody types differently and that statistics and AI algorithms can recognize users. I wonder though if they did testing on whether a user can be still recognized in the morning after a night of partying. In my experience I totally type differently then: very slow, and hitting backspace every other key... PSYLock is currently implemented in a Windows Logon library. Other integrations are planned including a Java applet for web site authentication.
More details on the PSYLock site.