Why astroturf? I mean, social media networks are naturally cyclical; the only thing they do is connect users, all the content comes from the users themselves, so the only way they can compete is by being free and not having figured out an annoying business model yet. Once they have to start making a profit, they are done for. Reddit and Twitter are about to hit/have hit that point. No astroturf here, plant some all-natural grass seed.

tildes.net comes to mind