I just noticed recently when clicking on a link on twitter.com that the URL I was sent to looked something like this:
It looks like Twitter is counting all clicks on links and even registering what user clicked the link. If I’m not logged in and click a link it says “userId=-1”.
Twitter is probably working on “Trending links” or something similar to display what links are popular at the moment, this week…
This doesn’t appear to have been implemented in Twitter clients like TweetDeck, not yet.