We know of several overlapping categories of Web Polygraph users.
Based on mailing list subscriptions, there are about 350 individuals from 200+ companies/organizations that use Polygraph and/or Polygraph results. A few users are also Polygraph sponsors.
Web Polygraph is a de facto benchmarking standard for the Web caching industry that has been used to test and tune most caching proxies. Polygraph is the benchmark of industry-wide cache-offs.