Twitter’s link service at http://t.co is used to better protect users from malicious sites that engage in spreading malware, phishing attacks, and other harmful activity. A link converted by Twitter's link service is checked against a list of potentially dangerous sites. When there's a match, users can be warned before they continue.
Our link service will also be used to measure information like how many times a link has been clicked. Eventually, this information will become an important quality signal for our Resonance algorithm—the way we determine if a Tweet is relevant and interesting.
[support.twitter.com...]
The post goes on to explain that bit.ly shortened links will continue to work and provide tracking data [webmasterworld.com]
Cookies, long the basis for tracking users, need web browsers to store them. In a world where we share URLs via email and social networks, those cookies get lost along the way, and with them the ability to track viral spread of a message...
Every time you access the Internet through a particular app -- Facebook, Gowalla, Yelp, Foursquare, and so on -- you're surfing from within a walled garden. If you click on a link, all the marketer sees is a new visit. The referring URL is lost, and with it, the context of your visit.
This is why short URLs are so important. URLs survive the share... That's why URLs are the new cookies.
Why Twitter's t.co is a game changer [radar.oreilly.com]
