SPDCA: The other direction.
I convinced myself that idkfa needed to have an "unread" feature. That is to say: after I spend incredible amounts of time getting the "read" part right, I felt I might find value in going the opposite direction. So now, instead of a "speedreading" feature, we also have a "un-reading" feature for marking certain posts as unread.
Like the speedreader, it's plugged into the search feature. Basically: search to find a data set you're happy with, whether it be an item, a thread (one of the icon links, if you're interested), a single post, etc., you can choose to mark it as read (speedreading) or unread (un-reading).
This helps me in a few ways:
I realize this probably isn't an absolutely necessary feature. But it makes the seen/unseen mechanism more complete, and gives you control over it to make it conform to the way you want to read a post.