We envision a future in which clouds of microcomputers can be sprayed in an environment to provide, by spontaneously networking with each other, an endlessly range of futuristic applications. However, beside the vision, spraying may also act as a powerful metaphor for scenarios such as ad-hoc networks and P2P computing. In this paper we: detail the different spray computers scenarios and their applications; discuss the issues related to the design and development of spray computer applications, calling for novel approaches exploiting self-organization and emergent behaviors as first-class tools; present the key research efforts being taken in the area; try to define a research agenda.