There’s been a lot of discussion of Wikipedia compared to encyclopedias (typically, the Brittanica); see, for example, this article by Stacy Schiff in the New Yorker. The only thing I’d like to add to this discussion is that Wikipedia and traditional encyclopedias aren’t that different as might be supposed. One of the features of Wikipedia is that people write the articles for free, just for the love of it. I’ve written several articles for encyclopedias, and it’s basically the same thing. They pay a very small amount, and basically the reason for writing an article is that I tihnk somebody might read it, and I’d like to inform them. The mechanism is clearly different from Wikipedia, and the traditional encyclopedia is not infinitely updatable etc., but it’s more wiki-like than one might think from the outside.