URL shortening is a technique in which a URL may be made substantially shorter in length and still direct to the required page. This is achieved by using an HTTP Redirect on a domain name that is short, which links to the web page that has a long URL. For example, the URL http://www.pagerank-plus.com/2011/06/how-google-treats-url-shorteners/ can be shortened to http://bit.ly/prplus or http://tinyurl.com/prplus. This is especially convenient for messaging technologies such as Twitter, which severely limit the number of characters that may be used in a message. Short URLs allow otherwise long web addresses to be referred to in a tweet. In November 2009, the shortened links on one URL shortening service were accessed 2.1 billion times.
Google does take URL shortner and passes the link juice unless there is a no follow tag. For social signals Google does consider URL shortner and ranking signals and the reason is because URL shortner works on the 301 redirection and follow the Google guidelines.
Unfortunately, a 301 redirect does not pass along all Pagerank. Pagerank will be downgraded through links including 301 redirects.
Google’s Matt Cutts addressed the issue in a video: