I'm not sure if it is significant, but I used to have a bunch of check boxes when I went to look at my unread posts / replies. I could check off the boxes of messages I had no interest in, then "Mark selected as read". I can no longer do this.
It might be a setting I've forgotten about or something of that nature. I'm using the "SMF Default Theme - Curve" Theme, if that means anything.
If there's a way I can get that back, please let me know.