I very much enjoyed reading this book, Wisdom of Crowds by James Surowiecki (kottke.org). Research has revealed that groups of people make consistently better decisions than individuals, as long as certain conditions have been met.
“If you ask a large enough group of diverse, independent people to make a prediciton or estimate a probability, and then average those estimates, the errors of each of them makes in coming up with an answer will cancel themselves out. Each person’s guess, you might say, has two components: information and error. Subtract the error, and you’re left with the information.”
The book describes the necessary conditions and discusses many examples. Many social communities and websites are based on these principles. For instance, You Tube or Slideshare use the ‘wisdom of crowds’ to filter out the most interesting content (not necessarily the most-viewed content).