At least not the way you phrased it. Individual posts are not marked read. Forums are timestamped read, and posts created/edited after that point in time are considered unread.

However, I was thinking of adding a 'mark forum read if possible after new post' deal, where if you add the only 'unread' (for you at least) post to a forum, then the forum gets marked read for you.

The ttl would have to be per-user for this to be effective, and I've already decided I'm probably not going to do per-post per-user read marks.