Brands create a pretend one.
Social media creates a real one, customizable to suit your level of interaction.
Life is lived among other people. When we experience pain, rage and love, the high of a lesson learned or milestone achieved, it is higher in community.
Brands do well when they create community. But not in a way that is at all obvious. And not to constantly push product.
The best thing a brand can do is create a platform around an idea, step back and let the interaction happen by itself.
People will expect the brand to sell them things, at some point - shopping and rating goods is a primary way we interact after all.
But it should always, first and foremost be about bringing people together. That and not the Marketing Department's version of an image is what makes the brand one-of-a-kind and (not unimportantly) uncopyable.
* All opinions my own. Photo of a community bulletin board in Starbucks by me.