Alex Bosworth talks about the collaborative process of Wikipedia and why it works. Collaborators come in different shapes and sizes, he says. Some of them work on one project that they know a great deal about, some of them love to edit, some of them drop in and contribute a little, some of them contribute a lot. That Wikipedia allows for all these different users and has ways to reward the high level contributors adds a great deal to its success:

The core mechanic for Wikipedia is both the thrill of editing a grand project collaboratively, and the more basic reward of having the power to be the expert in a subject that is near and dear. Wikipedia self-selects for people who are obsessive about various subjects or just editing in general, as in every case the person or set of people willing to hammer their edits obsessively will win power over the page, and thus the reward of participation. For controversial subjects where two groups are equally obsessive, this will work itself out in a compromise where only the most obviously provable details remain, such as seen in the common Controversy sections: "Among many, there exists a school of thought that Hitler was really just misunderstood". This compromise is otherwise known in the sometimes cryptic Wikipedia shorthand as of WP:NPOV, or Neutral Point of View.

In terms of the high level goal of Wikipedia being the sum of human knowledge, edit wars may be sub-optimal as some useful information provided by domain experts is overwritten. In optimizing for the most prolific editors, Wikipedia does not select for the most expert editor to win, or offer a reward for the most expert edit, instead the most widely acceptable edits among the mostly non-experts will win. This mechanic does however succeed in creating an environment where thousands of people are willing to make thousands of edits, creating a very wide and useful resource for many types of information, such as facts, basic details of concepts and controversial topics phrased in neutral tones.

...via Smart Mobs