In the advent of electronic health record (EHR) systems, physicians and clinical researchers enjoy the ease of storage, retrieval, persistence, and sharing of patient data. However, the way physicians interact with EHRs has not changed much. More specifically, task support for temporally analyzing large number of EHRs has been lacking. A number of information visualization techniques have been proposed to alleviate this problem. Unfortunately, due to their limited application to a single case study, the results are often difficult to generalize across medical scenarios. In this paper we present the usage data of and user comments on our information visualization tool Lifelines2 through eight different medical case studies. We generalize our experience into an information- seeking process model for multiple EHRs. Base on our analysis, we make recommendations to future information visualization designers for EHRs on common design requirements and future research directions.