The problem of designing and evaluating mobile computing applications is of growing concern in the HCI community, due in part to the difficulty of applying traditional design and evaluation methods to increasingly informal and unstructured usage contexts. We describe the design and evaluation of an integrated location-aware event and meeting planner built to work in a PDA form factor. We discuss the limitations and possibilities of location technology on mobile devices and how it can be used to create useful, usable, and elegant applications. We outline major design decisions, the results of qualitative formative evaluation performed with a small number of participants, and the second iteration of the design. Finally, we offer a number of general considerations on the design process and on specific issues related to mobile handheld applications, including reference metrics for design assessment, user training and cross-over effects from desktop systems.