Sorry if I missed this..
But is there a way so that it would only kick them back to the login page if they were inactive for x number of y (hours, minutes, whatever). So if they were actively browsing the Board (reading, posting, etc) they would not be forced to log-in again.
I hope that was clear (?!), either way this addition to your already super hack sounds very cool, if for just making them log in every time they close the browser
Damn the cookies!
Keep up the good work!