[Detective]

I think it should not be hard to code such a plugin. It would have to create a new database table, like bb_read, with the following fields:

– bb_user

– bb_post

– bb_last_comment_read

This way you could modify the posts query, left joining it with this table. If the join is NULL (please correct me if i’m wrong, i haven’t done these things in a lot of time), then the user has never read the post. If bb_last_comment_read is less than the actual number of comments or replies, then he hasn’t read the last post.

Another interesting alternative is what the folks at wordpress.org are doing … for non-visited links they have a font with a font-weight: bold style. So you can see which topics are new.