Are there any examples of a government department successfully using social media?

By social media, I mean things like Twitter, Facebook, MySpace, Youtube, blogs, and Wikipedia.
Any country or level of government is okay.
I’m doing a presentation and need some examples. Thanks.
Obama is an interesting example, but I’m thinking more along the lines of a department, rather than a specific individual or politician.

GovLoop – A Nest For Public Sector Workers

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GovLoop (www.govloop.com), also popularly known as the “Facebook for government”, is the premium social network for more than 22,000 people in and around government across the world. Federal, state, local and international public sector personnel connect and collaborate through blogs, forums, groups and many more web-based tools.

Launched in June 2008, GovLoop.com is becoming [...]