I know it hasn't been done. We had a similar discussion about it - but there are some issue with trying to do it I belive.
Here is the related thread.
I don't fully understand how the last post thing works. I know Rick has said that it's not really tracked on a per post basis. Thus it's actually the postlist.php page that marks the post read. That's why sometimes viewing the forum marks all the post in it read. He said it'd be too intense on large forums to track each post.
Although sometimes this appears to behave like it's individually being tracked. So......
Often viewing a post from the "last post by" link does not mark it read - because you bypass the postlist page. So if you had a page to display all the unread posts.... reading them from there probably wouldn't mark them read, as you're skipping the forums postlist page.
But it would be very cool if someone could make it work. I just don't think with the current architecture it would work correctly.
