At Interaction '11 in Boulder Colorado Dick Buchanan told us that an interaction is "how people relate to other people through the mediating influence of products."
Earlier, at Interaction '09 in Vancouver, Robert Fabricant told us, that "interaction design is not about computing technology." Instead, he argued that "Behavior is our medium."
These statements have become uncontroversial in the world of interaction design, and yet when we talk about design methods, we still talk about methods for designing products and for human-computer interfaces. We have a body of methods to design products (the "mediating influences") but very few tools and approaches available to work with the larger systems of interaction.
Recently though, we've seen teams having success with methods that blend Service Design, Lean Startup, and Lean UX methods into what I call "Learning From Live Systems" approach. By launching services early and powering them with a mix of software and human "concierge" services, teams are able to develop and test systems even as they are under construction.