In the last days there was an interesting and really fascinationg discussion about the exact definition of Government 2.0, that took place on Govloop, social netwotk of american government (http://www.govloop.com/group/government20club)
I feel that with all our effort to rationalize the contribution of Gov 2.0 to citizens and to government itself, we might forget one important, and in my eyes central element of Web 2.0 - that it's fun! I think that all things based on Web 2.0, including Gov 2.0, are fun. After all, This is social media - and people come to Web 2.0 to communicate because it's fun. They also come to Web 2.0 for advice, information, service and so on - but they are attracted into it because it looks attractive, light and funny. The Gov 2.0, therefore, must include this element. It will attract more people to dialogue and interaction. Governments are perceived as very "serious" and "heavy", so the element of fun must be there as well.
May be the word "fun" looks too amateur and simplistic, but as a practitioner of Gov 2.0 in the last two years I believe it's one of the key elements for Gov 2.0 success.
After all, the work we make will be more interesting and productive - if it's fun.
The twitter of British Foreign Ministry dedicated for british citizens abroad could serve as a good example of what I say: http://twitter.com/britishabroad