It’s no secret to anybody who knows me but I absolutely hate URL shortening services. My problem with them stems from the fact when you click on a shortened URL you haven’t a clue where it will actually take you. This gives you a great vector for an attack by linking somebody to a bit.ly link which sends an unsuspecting user to a malicious website that uses a browser exploit to infect their machine.
What I never thought about was using a URL shortening service to perform distributed denial of service (DDoS) attacks. Hit the link to details (which are actually pretty trivial).