As the re-posting of 'tweets' (micro blog posts to Twitter) using identifiers like RT (re-tweet) or # (referred to as a hash tag but more simply meaning related to this topic) get pushed out to more sites, more often; these short URL's act like blog postings or other inbound links. Inbound links is a key factor in generating higher ranking pages.
A Google Engineer in Quality Assurance has posted a great video on YouTube (show below) that explains how Google treats short URL's (with 301 redirects) like any other link directly to your site.
So use it wisely as another tool in your arsenal to assist your pages to rank higher. Although having good relevent content on the page to begin with to is certainly required prior to using these techniques.