We report on our experience in designing and evaluating seven applications from seven different domains using an interactive evolutionary approach. We conducted extensive evaluations for some of these applications, both quantitative and qualitative, and collected rich feedback from our ongoing collaborations with end-user scientists and artists. To ground our discussion, we refer to two applications, from art and science, as exemplars of our work in order to identify strengths and weaknesses in our approach. We argue that human-centered design could play an important role in addressing some of the identified issues such as the “black box” and the “user-bottleneck” effects. We discuss research opportunities requiring human-computer interaction methodologies in order to support both the visible and hidden roles that humans play in interactive evolutionary computation and machine learning.