In which I complain about the horrible, horrible people who run this site.
Yo Rob. Is it possible to fix the cookies, such that all threads don't all get marked as read when I log in after I have viewed the site unlogged in? Or maybe store the read/unread state server-side rather than through cookies, so that people will see the same thing when they log in from another browser/computer? Obviously, don't bother if it's going to be a big hassle, but consider this a "I will buy you several beers if you do this. And if I actually meet you. And if there is beer for sale when I do meet you" request.
I haven't been able to find a reasonable solution to what you're describing. Then again, maybe I'm misunderstanding the issue.