I think url-shortening is just a really bad idea in general. Certainly giving normal people the ability to track who clicks on their links is a good idea, but you don't need to obfuscate the url to do that. You could create a nice tracking service using urls like: http://digg.com/www.mysite.com/interesting-blog-post. The real cause of obfuscation is twitter's character limit, right? What does twitter gain by including anchor text in their 140 characters?