The Fels Institute of Government at the University of Pennsylvania has released a report titled Making the Most of Social Media: 7 Lessons from Successful Cities.  An overview of this good read:

[This] is written for local governments—cities, counties, townships and their affiliates—that are beginning to experiment with social media and would like to get more out of them. More than two dozen early adopters were interviewed for this report, and their experiences offer some lessons to local governments about what sorts of tools social media offer, how to integrate them into a busy office, and how to use them creatively to be more effective.