David Weinberger talks about The social life of echo chambers in KM Magazine:

There is certainly evidence that Internet traffic is chunky. Work by Albert-Laszlo Barabasi, for example, shows that networks, including the Internet, tend to generate clusters that get disproportionate amounts of traffic. And Clay Shirky found that traffic patterns for weblogs follow a "power law" in which a handful of sites generate a hugely disproportionate number of links. This topology isn't surprising once you think about it, although it's one of those predictions that's much easier to make afterward, if you know what I mean.

Even so, that doesn't tell us that the Internet is closing minds instead of opening them. David Sifry, the creator of Technorati.com, a site that indexes and ranks 1.6 million weblogs, points out that even though there is a power curve, if you rank blogs by how many sites link to them, the 100,000th blog has five links pointing at it. Five isn't a thousand, but it still means that five people with sites think enough of that 100,000th blog to recommend it to others. Presumably, that site is important to a small cluster of people. That's a readership that didn't exist before the Net. Further, if you add together all of the blogs in the "tail" of the power curve, it's a hell of a lot of blogs and a hell of a lot of readers. So, while the head of the power curve feels familiar to us because it's essentially a bunch of online columnists, the long tail is something new and unfamiliar: a galaxy of people who are finding constellations of readers, ready for ideas and conversation.