A Sphinn thread has discussion around a "quick" study done to test if URL shortening services like TinyURL and others pass any link value. Clearly, all the time you and I spend on services like Twitter, makes this question something that many SEOs and webmasters want to know.
The study said that these services do not pass link value. Some don't believe the study, some do. I won't be getting into the validity of the study. Do your own tests and prove it to yourself.
I do know that Googlers often say in the Google help forums to use URL shortening services when they don't want to share their specific URL. The reason, I don't think is about passing "link juice," but rather that they can expire the URL shortened version, so it does not return a redirect for that URL, where they can't do the same if they link directly to their web site URL.
That being said, and I know a lot of you spend a ton of time on Twitter and services like it that use URL shortening services. Do you want those services to pass link value? There are two possible ways the services won't pass the link value. Either the service themselves marks the links as nofollow or something like it or search engines decide on their end to not let them pass value.
Should they pass value? Take the poll:
Forum discussion at Sphinn.