I guess the fact that Twitter employees use bit.ly to map from short url:s to slightly longer url:s even in mails means something, but I'm not sure what.

(the http://bit.ly/sitestreams_doc link goes to http://dev.twitter.com/pages/site_streams)

I assume they just do it to track clicks.

Hm.. has any one hacked up some fancy visualizations using their framework yet?