After threatening as much for many months, Joshua Schachter has published a piece about how URL shorteners (TinyURL, bit.ly, is.gd, etc.) suck for everyone except the companies which build URL shorteners.
There are three other parties in the ecosystem of a link: the publisher (the site the link points to), the transit (places where that shortened link is used, such as Twitter or Typepad), and the clicker (the person who ultimately follows the shortened links). Each is harmed to some extent by URL shortening.
I agree with Schachter all around here. With respect to Twitter, I would like to see two things happen:
1) That they automatically unshorten all URLs except when the 140 character limit is necessary in SMS messages.
2) In cases where shortening is necessary, Twitter should automatically use a shortener of their own.
That way, users know what they're getting and as long as Twitter is around, those links stay alive.