The vision of ubiquitous computing suggests that interactivity will be embedded throughout our physical environment in a wide variety of modes of use and form factors. I will present a series of projects which exploit sensing technologies such as computer vision to enable a wide variety of fluid, natural interactions situated on walls and tabletop surfaces. For example, PlayAnywhere is a compact tabletop projection-vision system which explores a number of new interactions on everyday surfaces, while TouchLight combines a transparent projection screen material with computer vision techniques. These new form factors have the potential of changing the way we relate to computing, but they also pose a challenge in terms of interaction design because they are so different from today's desktop computing.