An interesting phenomenon, noted by many, is that most content in user-contributed content venues (including online communities that focus more on “community” than on creating a durable information resource) is provided by a small fraction of users. Many have documented that participation in a wide variety of voluntary settings follows a power law (that the amount of contribution decreases proportional to 1 over the rank of the contributor).
Jakob Nielsen offers a nice summary including some historical references:
In most online communities, 90% of users are lurkers who never contribute, 9% of users contribute a little, and 1% of users account for almost all the action.
This sort of participation inequality has been seen in online communities, Amazon book reviews, Wikipedia edits, blogs, and peer-to-peer file sharing networks, to name a few venues (for the latter, see E. Adar and B. Huberman, “Free Riding on Gnutella”, First Monday, 5 (2000), and S. Sariou, P. Gummadi, and S. Gribble, “A measurement study of peer-to-peer file sharing
systems”, Multimedia Computing and Networking (January 2002).)
Inequality isn’t directly an issue of “getting good stuff in”, as much as about getting stuff in at all. But of course, the quality of contributions is going to depend on who is motivated to contribute, not just how many contributors there are. Thus, the problem of getting critical mass for a user-contributed content service is not just getting enough contributors, but getting the right contributors.