Yeah, that's certainly one way to improve the signal/noise ratio of a social networking site, but it simply can't scale to the size of say, Facebook or Twitter.

Yeah, that's certainly one way to improve the signal/noise ratio of a social networking site, but it simply can't scale to the size of say, Facebook or Twitter. Human moderation is simply too slow and expensive to be done on an 'industrial' scale, and charging money will always significantly limit a site or service's audience. Then again, perhaps the unfortunate truth is that something on the scale of today's mainstream social networks is simply unworkable. Perhaps at a certain size a community site simply falls apart, and nothing short of human level AI will be able to keep it intact.