Apparently at last years Davos gathering, when Mark Zuckerberg was asked by one of the assembled media moguls how to create a community he told them you can't. Communities already exist. Instead, think about how you can help that community do what it wants to do.
"the powerful are, no surprise, one step behind in their understanding of the true significance of the internet: They think it is all about individual action when, in truth, it’s about collective action."
The internet will shift power more than most people think. As Jarvis goes on to point out, if you think the internet is about individualism you fear it's anarchy. But if you realise it's about connections and collective actions "you come to see that institutions will reform, that they will become fluid and ad hoc, like the parliamentary system of multiple parties joining in coalitions to rule."
Communities work in particular ways, and online communities are no exception. The 1,9,90 rule of social media means that a relatively small proportion of the community will be by far the most active – if you're a social media owner these will be your superusers, if you're a brand these will be your fans, if you're both (as most brands surely will be) these will be your advocates.
Less than two weeks ago the 10 millionth article was written on wikipedia. It's an amazing thing. I've heard that Jimmy Wales defines the Wikipedia community as (and I'm paraphrasing here) "One part anarchy (anyone can contribute anything), one part aristocracy (the wikipedia superusers), one part democracy (voting on disputes), one part monarchy (him)". Brands that tune into this kind of thinking will win.