Science gateways, also known as advanced web portals, virtual research
environments, and more, have changed the face of research and scholarship
over the last two decades. Scholars world-wide leverage science gateways
for a wide variety of individual research endeavors spanning diverse
scientific fields. Evaluating the value of a given gateway to its
constituent community is critical in obtaining the financial and human
resources to sustain gateway operations. Accordingly, those who run
gateways must routinely measure and communicate impact. Just as gateways
are varied, their success metrics vary as well. In this survey paper, a
variety of different gateways briefly share their approaches.