Although Facebook is the largest social network site in the U.S. and attracts an increasingly diverse userbase, some individuals have chosen not to join the site. Using survey data collected from a sample of non-academic staff at a large Midwestern university (N=614), we explore the demographic and cognitive factors that predict whether a person chooses to join Facebook. We find that older adults and those with higher perceived levels of bonding social capital are less likely to use the site. Analyzing open-ended responses from non-users, we find that they express concerns about privacy, context collapse, limited time, and channel effects in deciding to not adopt Facebook. Finally, we compare non-adopters against users who differ on three dimensions of use. We find that light users often have social capital outcomes similar to, or worse than, non-users, and that heavy users report higher perceived bridging and bonding social capital than either group.