The use of digital products and services has expanded from largely instrumental, work-oriented settings to include entertainment, leisure, personal communication, and other classes of hedonistic use. The development of foundational concepts in the interaction design community to succeed usability and utility has lagged behind considerably. I argue that interaction design would benefit from attempts to articulate experiential qualities of digital products and services, and illustrate the approach by presenting the concept of fluency. It refers to the degree of gracefulness with which the user deals with multiple demands for her attention and action, particularly in augmented spaces where the user moves through shifting ecologies of people, physical objects, and digital media. I develop the concept of fluency by analyzing a range of digital artifacts in use situations, addressing the main themes of (1) social norms and practices and (2) peripheral interaction and calm technology. In terms of research methodology, this paper illustrates how design and criticism can be merged to construct elements of transferable knowledge for communication with design-research communities.