No, not that complicated-- just like somewhere there would be a link to "Read new messages" and it would link to a function that shows all unread threads from every forum. The DCforum one that I'm used to lists threads that are new or have new posts divided by forum. I've attached screen shots of theirs so you get an idea.
While I'm at it, but kind of on the same topic, a user has requested that posts not be marked read unless they manually click the mark link. It'd be easy enough to define their preference in the user profiles, but again, I can't figure out how read new works (it seems some of it is in the database and some is in a cookie?)
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