Since we are talking about "keystyle" recognition as a security measure I don't really see how you can stop me from using your machine.... See, I'll have physical access, won't I. If I boot to safe mode, disable the service, reboot, do my dirty work, reboot to safe mode and re-enable the service and reboot again I have used your computer despite your security measures.

Nice idea to keep normal users off a machine at work but I find the password protected screen savers do that well enough. You are not going to keep anyone with physical access off the box if they have even fairly minimal computer knowledge.