Galaxy clusters furnish extremely rich information on the contents and structure of our universe. The potential of galaxy cluster studies to constrain dark energy, for example, motivates a number of ambitious cluster surveys. Among these, surveys based on the Sunyaev-Zel'dovich (SZ) effect are particularly powerful for their ability to cleanly select clusters out to redshifts z>1. Now poised to begin surveying substantial areas of sky, dedicated interferometers, bolometer cameras and the Planck satellite will soon produce large cluster catalogs that will provide a precise measure of the cosmic expansion rate over a range of redshifts and precipitate a new understanding of structure and galaxy formation. I review the science potential of these surveys and examine some issues of SZ cluster catalog construction.