There is a growth in the popularity of social file sharing systems. This paper describes the design of Cattail, a social file sharing system for the enterprise. Through a'Recent Events' stream, Cattail supports social navigation and exploratory search by inferring relevant social connections rather than purely relying on user-specified contacts. Social navigation is further supported through pivot browsing from a consolidated history of user actions on an individual's files. Through usage log analysis over an 8- month period, we found that Cattail's novel network inference and social navigation features enabled a net gain of clickthroughs. Interviews with users revealed that this led to increased discovery of relevant people and content. We conclude with a discussion of several possible enhancements to the system. Findings from our research provide a strong foundation for the design of social file sharing systems for enterprise settings. Copyright 2011 ACM.