Count of eyeballs that your post has passed through. I think they could put a "mark as read" thingie which could then count how many people marked as read. - TrafficBug

kind of interesting how Twitter gave the ability to make lists public. More of a marketing gimmick, but at least it's something. - Vincent van Wylick

I think this would be a wanted feature in twitter too. With people following hundreds of people, their attention span is limited to the first few tweets that they seem to eyeball, so it would be good to know just how many eyes' visibility span your message has passed through. - TrafficBug