The document summarizes research on quantitative analysis of user-generated content on the web. Key findings include: 1) The distribution of user-generated content supply has a heavy tail and follows a Lotka or Weibull distribution, meaning there is no average user and a small number of users generate most content. 2) The production of different types of user-generated content is similar statistically but not identical. 3) The "Pareto principle" (80/20 rule) applies to user-generated content production. 4) Measuring user-generated content is important to test hypotheses about how it is produced and to gain insights for managing sites dependent on this type of content.