[userbinator]

Consider what happens when someone decides to give it a URL that redirects infinitely -- it is possible to make an infinite loop, as someone demonstrated 4 years ago while also complaining about URL shorteners:

http://breakingcode.wordpress.com/2010/01/11/having-fun-with...

(The infinite loop in that example unfortunately seems to have broken, illustrating another downside to URL shorteners - they can go away rather quickly.)

[oneeyedpigeon]

Detect the loop and reject the URL. I'd rather twitter protect me from ever clicking on an infinitely-redirecting link, although browsers tend to handle that case fairly gracefully.