[Surowiecki] rejects the widespread view that groups of ordinary people are usually wrong--and that we do better to ignore them and follow experts instead. Even when individuals blunder, he believes, groups can excel: "Under the right circumstances, groups are remarkably intelligent, and are often smarter than the smartest people in them." This is so even when "most of the people within the group are not especially well-informed or rational." What is wonderful, and surprising, is that "when our imperfect judgments are aggregated in the right way, our collective intelligence is often excellent." Instead of chasing experts, we should consult that collective intelligence.
...Surowiecki also invokes an astonishing finding by the British scientist Francis Galton, who tried to draw lessons about collective intelligence by examining a competition in which contestants guessed the weight of a fat ox at a regional fair in England. The ox weighed 1,198 pounds; the average guess, from the 787 contestants, was 1,197 pounds.
...Surowiecki does not make the implausible suggestion that all crowds are wise. To qualify as such, a crowd needs to satisfy three conditions. It must be diverse; its members must be independent; and it must have a "particular kind of decentralization." Each of these conditions is designed to ensure what most interests Surowiecki, which is the emergence and the aggregation of information that group members have.
This reminds me of Rousseau's Social Contract, written centuries earlier. Rousseau advocated a form of direct democracy, whereby each citizen votes for what they believe to be in the common interest. He thought individual mistakes in either direction would tend to cancel each other out (like with the contestants guessing the weight of the ox), so the average result would accurately represent the "general will".
What especially caught my attention here was how similar Surowiecki's "conditions" are to Rousseau's own. Rousseau explicitly denounced political factions because they encourage clusters of people to all vote the same way - that is, it reduces diversity. He also wished to ensure the independence of all voters, recommending (bizarrely) that they not be allowed to communicate or discuss the issues with each other. I'm not sure about decentralization: that one at least sounds like a more modern idea.
Anyway, I just thought I'd point out those parallels. There's also some intriguing speculation about the viability of "prediction markets". Sunstein's balanced critique of Surowiecki's ideas in the latter half of the article is especially worth reading, and pre-empts most of the complaints that sprang to mind as I read the first half.
Update: Blogger has a spin-off: The Wisdom of Blogs