Although research on the social aspects of virtual (or synthetic) worlds abounds, the role of the client-side applications (viewers) used to access these worlds is often overlooked. This thesis examined the interfaces of several popular third-party viewers (TPVs) used by Second Life (SL) residents in an attempt to formulate recommendations for future user-centered viewer design endeavors. The Uses and Gratifications theory was used to identify goal-based user groups in SL. Data collection began with an online survey of 540 frequent SL users; a cluster analysis of the resulting data revealed six distinct groups: socializers, gamers, developers, designers, business communicators, and entrepreneurs. Residents from each identified group were then interviewed to discover the strengths, weaknesses, and relative usability levels of their primary viewers of choice from their group’s perspective. Findings indicated that (a) all groups tended to have similar opinions regarding the strengths and weaknesses of SL viewer UIs, (b) users overwhelmingly preferred viewers based on Linden Lab’s 1.x viewer, (c) most SL viewers tended to have inadequate inventory management tools, (d) the Phoenix viewer was most often cited as having the best content creation tools, and (e) many complaints about the SL user experience related to server-side issues or world design rather than the client application. In conclusion, future research recommendations are discussed.