Hi!
This monday I received my two YubiKeys and I started a bit playing with it. My mainly used OS is OpenBSD (on Desktop, Firewalls, Servers and Notebooks) and I searched for a solution to securely login. That's where YubiKeys come in to play...
After a few lines of code I finished a first attempt of logging in with OTP YubiKey tokens, checked and verified to a
local database. No network connection or external service is needed.
If you want to try it out, the source code of the auth plugin named "login_yk" is found here:
http://www.h-ein.de/projekte/yubikey-login-auth-module-openbsd.html (sorry, german only).