We investigate in which forms field trials are a workable model as part of an exploratory design process for sporadic, mobile, non-work settings. A major concern of evaluating ubicomp systems is to study how practices and context of use emerge and develop over time when new technology is introduced. To introduce a sophisticated version of our own prototype in the course of an iterative design process, we conducted a public field trial of the system—a new platform for mobile democratic discussions in municipal planning—that we distributed via the Android Market. However, it turned out to be surprisingly difficult to evaluate our design in a setting that stretches over time, place, and without a preselected set of users. Analyzing our difficulties, we develop a general model for methods studying ubicomp systems. On the basis of this model, we characterize an openly interactive approach to field trials in order to look ahead rather than back.