I found vulnerabilities in two social gaming networks that let you take control of people's Facebook and Twitter accounts using _just_ the UDID. I never published the details of these vulnerabilities, but you can find an official acknowledgement from at least one of these companies (Chillingo of Angry Birds fame) in this WSJ piece:
http://blogs.wsj.com/digits/2011/09/19/privacy-risk-found-on...