This was a talk given by Jenny Wong and Danilo Sato at Agile Brazil 2011:
Agile teams learned that splitting teams into silos and functional areas is not a productive way to develop software. Having cross-functional teams improve collaboration and enables delivery of value faster. The same arguments can be applied to user stories. The way in which business requirements and features are translated into user stories play an important role on the software delivery process. This session will discuss the benefits of working with small user stories, and present different ways to split requirements into user stories.