A new type of Web-based applications, known as Enterprise Mashups, has been gaining momentum in the last years. Novel design principles are currently about to emerge allowing to cover the long tail of user needs and to provide individual and heterogeneous enterprise applications in a shorter time. In this paper, we introduce the main components of this new paradigm, and discuss the design principles of the architecture (Enterprise Mashup Stack), upcoming intermediaries and mass collaboration, lightweight composition as well as perpetual beta development model.