A new kind of Web-based application, known as Enterprise Mashups, has been gaining momentum in the last years. Enterprise Mashups implicate a shift concerning a collaborative software development and consumption process. End users combine and reuse existing Web-based resources within minutes to new value added applications in order to solve an individual and ad-hoc business problem. Novel design principles are currently about to emerge allowing to cover the long tail of user needs. In this position paper, we introduce the terminology used in context of this new paradigm and present an Enterprise Mashup Stack which consists of three layers: Web-based resources, widgets, and Mashups. Based on this model, we elaborate on the design principles of upcoming intermediaries and the mass collaboration form, the lightweight composition style as well as the perpetual beta development model. By means of the EU funded research project FAST, we show their real-world applicability.