In the UK, the existing social structures like the church had pretty much collapsed before social networks came on the scene.

Social networks actually have the potential to help restore local social structures as at root they are about connectivity. A local volunteering group can easily keep its members up-to-date via its FB group. A local Councillor can update his constituents via his Twitter account. I'd like to see a new batch of startups which work on channelling social media usage to properly social ends.