People are seeking more meaningful and customized information than what is obtained by keywords-based queries and document retrieval through a search engine. In this paper, we look at a set of such services, referred to as social Q&A sites. With sites such as Google Answers, and primarily Yahoo! Answers, we attempt to understand various characteristics of user participation and their possible effects on the design and success of the site. We discuss these social Q&A sites by comparing their designs based on user participation and point out the effects and defects of each. We show that active user participation is the core component of these sites. We further analyze rich data collected from more than 55,000 Yahoo! Answers user profiles to understand the nature of user participation, and the quality of this participation. With our analysis we discover that Yahoo! Answers model implicitly encourages users to make an active contribution. An important contribution of the work reported here is the framework with which various factors relating to user participation in social Q&A sites can be studied.