We present experiences as artists and Human-Computer Interaction (HCI) researchers exhibiting an interactive artwork called Tweetris at a public event, and its simultaneous research evaluation. We describe the unique opportunities a public art event offered for achieving our research goals, then discuss three key challenges we encountered: tensions between creative and research goals before the event, ethical considerations during the event and in analysis, and obstacles complicating subsequent evaluation as the work has evolved. We offer observations throughout that are important to consider when conducting HCI research at public art events.