The Long Tail weblog has some interesting things to say about wikipedia and other stuff (and scroll down to the comments for a good discussion).

...these systems operate on the alien logic of probabilistic statistics, which sacrifices perfection at the microscale for optimization at the macroscale.
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When professionals--editors, academics, journalists--are running the show, we at least know that it's someone's job to look out for such things as accuracy. But now we're depending more and more on systems where nobody's in charge; the intelligence is simply emergent. These probabilistic systems aren't perfect, but they are statistically optimized to excel over time and large numbers. They're designed to scale, and to improve with size. And a little slop at the microscale is the price of such efficiency at the macroscale.
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Probability-based systems are, to use Kevin Kelly's term, "out of control". His seminal book by that name looks at example after example, from democracy to bird-flocking, where order arises from what appears to be chaos, seemingly reversing entropy's arrow.