GovLoop isn't a social network, it's a forum site that uses Web 2.0 social-media tools. True social networks connect people across site/service boundaries. They're about people and communications, facilitated by sites that include GovLoop but not constrained within any one site. But that's quibbling about definitions.
Further, I like GovLoop, but it's highly US centric and not the *anything* for government or Government 2.0 in general.