C. Shalizi has many useful things to say, and to link, about "the wisdom of crowds", partly in response to something I posted a while back.
Shalizi includes a pointer to a Rational Herds: Economic Models of Social Learning (ISBN 052153092X). Aside from having really cute penguins on the cover --- reason enough to buy most books --- the book also looks intellectually fascinating, and instantly makes my to-read list, though with my recent binge of book-buying  I most likely won't get around to reading it anytime soon.
In related news, I actually read/skimmed large chunks of The Wisdom of Crowds whilst browsing during the aforementioned book-buying binge. I concluded that the book itself (as opposed to the publicity, or the vulgarized versions of Surowiecki's thesis that are making the rounds) is not exactly bad, but rather good, yet frustrating. Surowiecki's tackling an important subject. He writes with the fluency and accessibility you'd expect from a New Yorker writer. The book recounts many fascinating anecdotes, and it even lays out a set of criteria for organizing "wise crowds" that's sensible and convincing (though stated too vaguely for my tastes). But these strengths make the book's failures all the more disappointing. Each chapter contains at least a few things that get my ersatz-scientist hackles up: an overgeneralization from meager data, or an incomplete and vague summary of a more systematic study, or an example cherry-picked to support his point without adequate treatment of counterexamples . The best ideas in Surowiecki's book aren't new, and the intellectual frame he puts around them often adds little . Lastly, and perhaps most importantly, as Shalizi writes in the post linked above, although Surowiecki does give a nod to the difficulties of crowd organization, in general he does not place enough emphasis on it.
My guess, therefore, is that readers genuinely interested in the ideas Surowiecki discusses would be better off reading the primary sources in Surowieki's acknowledgments. I don't have a copy handy, and I regrettably forgot to scribble them down. Oh well. Next time I'm in a bookstore...
Bonus link: Radio National interview with Surowiecki.
 At the Cherry Creek Tattered Cover in Denver, last week, while visiting a friend; the bargain shelves should be labeled with warnings for compulsive verbivores.
 For example, one form of "crowd wisdom" that Surowiecki returns to several times is the fact that groups of people appear, in aggregate, to be very good at estimating quantities. One of Surowiecki's stories in support of this claim: in 1906, economist Francis Galton found that crowd of people at a fair were collectively able to estimate the weight of a thousand-pound-plus ox to within one pound, better than any individual in the crowd. He has a few more examples in this vein, but almost no discussion of the abundant counterexamples. For example, experiments show that, on average, people consistently overestimate the height of men and underestimate the height of women, even when they're shown photographs of the subjects standing next to common reference points. Surely a trained surveyor would do much better than a crowd in this case. Surowiecki briefly mentions some studies wherein experimenters were able to skew estimation results by using explicit suggestion, but he ignores systematic, consistent, a priori bias --- which gives the reader the impression that estimation bias is something induced in relatively rare and peculiar circumstances.
 Returning to the collective estimation problem in the previous footnote: the success of averaged estimates would lead me to conclude that the human senses can measure accurately, but with a random error that follows a symmetric (Gaussian?) distribution. This is interesting, but it says little about the "wisdom of crowds". Instead, it testifies to the value of repeated measurement, a bog-standard part of scientific orthodoxy. You will get similar results with inanimate scientific instruments (e.g., a thermometer or a light-sensitive CCD) operating near the limits of their precision: measure many times, and you get a better, rounder bell curve than if you measure only a couple of times. Surowiecki's framing seems simply superfluous here.