@aral Hmm. I think I disagree, rather strongly — because relationships in aggregate, if dense enough, form something new. Community is an emergent property, but it's a thing on its own, semi-independent. We saw how fragile the peer-to-peer relationships only was when the blogosphere was harnessed into the social media machine.
I've always been fond of online places, and thought we needed more of them. But the forces of centralization and corporatization sure made a mess of it. Reddit is such a stunning example of both good and bad. So much hate lived there in some communities; but communities there existed somewhat independent of reddit. Their level of editorial control was fascinatingly hands-off for the most part. Ultimately the power structure poisons it, but I don't think the flaw is in it being place-like, just in governance gone bad.
I think the biggest problem is that communities _do_ have some boundaries, and that's good. Shared identity is one aspect that's hard to replicate with just a network of relationships. Sometimes this makes cliques of exclusion, but also it can build solidarity and a sense of collective purpose.