The Obama administration is using Drupal (an open source software project) for the government's 2.0 recovery website. Great. recovery.gov
With Drupal being used on such a nationally recognized site, a gigantic government one, it should be proof that it is enterprise ready.
My last gig was for Sony BMG/Music. We used drupal extensively for internal projects (collaboration and innovation projects) and external ones. The external Drupal projects were for Sony artists sites. From www.pinkspage.com to bobdylan.com and www.beyonceonline.com.
From Tech President "Why the White House's Embrace of Drupal Matters". "Drupal developers are abuzz with the realization that the White House's new Recovery.gov site was built using the free and open-source content management platform Drupal. Pre-Recovery.gov, the perhaps highest-profile use of Drupal had been the Onion website. But that's not the only reason that Drupal fans are excited."
On a smaller scale, I also used Drupal to help a Texas political consultancy develop www.bigredtent.com. It is a social network/community site for raising money for republic candidates. We also, used drupal to develope several individual gov 2.0 state sites in Texas.
From The Buzz Bin, "Government 2.0". Social media creates an open means of conversation between different government agencies and provides the government with new ways of reaching the public; it is an evolution in the democratization of government. Through social media, collaborators are able to create, organize, share and edit web content." This article is loaded with good ideas and links on social media in government.