Chances are if you do much online searching, you've visited a Wikipedia entry once or twice. Dan Gillmor has a good article on the wikipedia is and how it's done.

Wikipedia (www.wikipedia.org), an encyclopedia created and operated by volunteers, is one of the most fascinating developments of the Digital Age. In just over three years of existence, it has become a valuable resource and an example of how the grass roots in today's interconnected world can do extraordinary things.