URL shortening services are great, and they help you make the 140 character cut off. But, they are dangerous as a consumer as you don't know where they are going. You could get Rick Rolled, or worse. This is why I wrote the Endpoint Resolver library, and the Greasemonkey script that flips the URLs to the full ones in your Twitter stream.

Check out almaer.com/endpoint for more details, and the full code is hosted at Google Code here: code.google.com/p/endpoint-resolver