Using twitters web interface I clicked on this link http://bit.ly/olSOg and below are the abbreviated headers that I saw:
GET /link_click_count?url=http%3A%2F%2Fbit.ly%2FolSOg&linkType=web&tweetId=3540807536&userId=2533331 HTTP/1.1 Host: twitter.com ...
HTTP/1.x 302 Moved Temporarily Date: Tue, 25 Aug 2009 19:30:15 GMT Server: hi Last-Modified: Tue, 25 Aug 2009 19:30:15 GMT Status: 302 Found Location: http://bit.ly/olSOg
...
GET /olSOg HTTP/1.1
Host: bit.ly
...
HTTP/1.x 301 Moved Permanently
Server: nginx/0.7.42
Location: http://www.wired.com/entertainment/theweb/magazine/17-09/ff_craigslist_makeover