Hilary Clinton launched the US State Department's 21st Century Statecraft initiative earlier this year, using of course social media to spread the word and engage the different target audiences of Public Diplomacy.
This video clip can be found on the US State site, on YouTube and on Facebook
One of the central themes of this initiative, according to Richard Boly, Director of the Office of eDiplomacy, is that the traditional engagements of public policy - Government to Government, and Government to citizen - can be 'sliced and diced' in myriad ways using social media. Interviewed at the 2010 IFDT conference in Malta, Boly described how he and his colleagues are promoting the value of social media tools as "a natural extension of what we do as diplomats and how it can make us more successful". He stressed the importance of engaging experts outside the specific public diplomacy field and also of trusting the "bright, competent young people" who are employed in Diplomatic Services.
US State Department guidelines for Diplomats using Social Media, are also available on the open web, as are examples of their more experimental work such as using blogtalkradio as a channel