Instead of going to the index and clicking on "mark all forums as read", from the "unread posts" page enable an option to mark individual threads as having been read. As it is now you read a thread and then have to sort through the same long list of unread posts to find the ones you actually want to read. By eliminating the ones you don't want to read when you first go to "unread posts" it will save having to sort through them repeatedly.
Also, when you are reading a thread, have the option to go directly to "unread posts" instead of having to go back to the board index first.
Hope that was clear.