McKinsey just published a great study on How companies can make the most of user-generated content .
Findings of the study were:
1. The contributions of a small percentage of website members get engaged with the site and produce content.
2. Over time, participation rates throughout the user group increase. In 2004, for example, 90 percent of the contributions to Wikipedia came from just 2 percent of its users; by 2006, the top 2.5 percent of them were responsible for only 60 percent of all new content.
