Organizations that want benefits from social network tools will need to make some selective, deliberate and thoughtful choices that are different from the most highly restrictive "need to know" policies. For some more high-level thoughts on the relationship between social network and the org chart, see some high level thoughts on that topic, see: http://www.alevin.com/?p=1280
Twitter told developers explicitly that they should stop making third-party clients.
According to Twitter, Repeated privacy policy violations and an inconsistent user experience are the reasons for implementing these restrictions.