OK - If you login using your default forum username and you accidently close the window... so when you try to login again it tells you that you're already logged in... there is now a link on that page you can use to logout. It seems that would work for most people. Worst case? Re-register under a new name I guess. Currently the inactivity auto-logout is 90 minutes.

I'm not really the chatting type so let me know if something needs tweaking.