I often compare the "peer production" of Wikipedia to that of the OED, which was also built with the contributions of hundreds of people from all walks of life. I just finished Simon Winchester's The Meaning of Everything: the Story of the Oxford English Dictionary -- an excellent complement to his earlier The Professor and the Madman -- and note that the following could perhaps be said of Wikipedians as well:

... but we do not really know why so many people gave so much of their time for so little apparent reward. And this is the abiding and most marvelous mystery of the enormously democratic process that was the Dictionary -- that hundreds upon hundreds of people, for motives known and unknown, for reasons both stated and left unsaid, helped to chronicle the immense complexities of the language that was their own, and that they dedicated in many cases -- such as the Thompson sisters did -- years upon years of labour to a project of which they all, believed by some set of unfathomable and optimistic notions, insisted on becoming a part. (Winchester 2003:215)