Software reuse is regarded is as a key software development objective leading to reduction of costs associated with software development and maintenance. However, there is mounting evidence that software reuse is difficult to achieve in practice, and that software development approaches such as component-based development, and more recently service-oriented computing have failed to achieve anticipated levels of reuse. In this paper we identify the determinants of service reusability and argue that the design of services plays an important role in achieving high levels of reuse. We examine the relationship between service granularity and reuse and note that extensive use of coarse grained, document-centric services by SOA practitioners makes achieving reuse particularly challenging.