URL shorteners are evil. It's the digital equivalent of stepping into a car driven by a stranger, blindfolded. You don't know where you're going before you're there. It might not necessarily be a pleasant place.
With bit.ly, the link is much shorter with 21 characters, http://bit.ly/j8IpC8, and I'm left with 119 characters to describe the link in a twitter message.
Oh, and I'll know how many people clicked on my bit.ly link. I've become addicted to that feature.
Dammit i missed april fools day to announce my 'tweet compression' service :(
It would be better if Twitter offered their own way to shorten URLs (or have a separate limit for URL length), so that you could still see where the link pointed before clicking on it.