If Twitter's behaviour for elongating the URLs in the public Tweets is any indication, their own bots actually download the contents of the links, allegedly trying to scan it for malware or whatnot.
I, personally, suffer because I never experience any URLs being shortened, they instead only get elongated by the service, reducing already constrained character space.
I mean, you don't have to go far to find a URL shorter than http://t.co/qLxImbQYvn. Even if you have a newly registered .com, it's still likely they'll only elongate it if you ever post a link to it.
And Twitter should really change the name of their subservice disservice to be more technically accurate.
The CEO of Sonic.net is especially annoyed (and rightly so) -- he can't even refer to his company without getting an elongation!