Community Can't Be Faked.
Amid all the talk about communities and great examples like NIke +, there's a groundswell developing around the idea that you can build communities. I'm not sure you can. Running clubs, after all, are not new.
People are social animals and thus communities will form naturally around many products and services. The trick is to recognise this fact and concentrate on facilitating that natural formation rather than trying to artificially change behaviour.
Find the areas around your product/service where communication (the root of community) already exists. Focus on reducing any barriers to entry that are based upon elitism, fear and ignorance. Enhance inclusivity. Simplify and guide. But don't lead and control.
If somebody asked you to join a community that you'd hadn't previously coveted, wouldn't your reaction be the same as Groucho who famously refused to join any club that would have me as a member?
Addendum: Adriana tells of a real-life example that shows the perils of interfering in communities.