The Virtual Notebook System (VNS) is a distributed collaborative hypertext system that has made a successful transition from research prototype to commercial product. Experience in developing and deploying the VNS in diverse settings including biomedical research, undergraduate education, and collaborative system prototyping has developed insight into the use of systems for computer-supported cooperative work (CSCW). This paper provides a brief overview of the VNS, discusses some of its strengths and weaknesses with respect to collaboration, and draws some conclusions about the impact of metaphor and extensibility on the collaborative process.