LinucksGirl writes to share an IBM DeveloperWorks article that shows how to support user verification through keystroke-dynamics processing by modifying the GNOME Display Manager
(GDM). You can create and store a one-way encrypted hash of your keystroke patterns when entering your user name. The article shows how to add code to GDM to read current keystroke patterns and permit a user to log in when the characteristics are a match. An interesting idea to be sure but I know I certainly am not that consistent when I type, so I'm skeptical of how well this may work.