The proliferation of affordable mobile devices with processing and sensing capabilities, together with the rapid growth in ubiquitous network connectivity, herald an era of mobiscopes: networked sensing applications that rely on multiple mobile sensors to accomplish global tasks. These distributed sensing systems extend the traditional sensor network model, introducing challenges in data management, data integrity, privacy, and network system design. Although several existing applications fit this description, they provide tailored one-time solutions to what essentially is the same set of problems. It's time to work toward a general architecture that identifies common challenges and provides a general methodology for the design of future mobiscopes. Toward that end, this article surveys a variety of current and emerging mobile, networked, sensing applications; articulates their common challenges; and provides architectural guidelines and design directions for this important category of emerging distributed sensing systems. This article is part of a special issue on Building a Sensor-Rich World.