KIE (www.kie-services.com) is using JSPWiki on its own intranet, and on a couple of major Italian law firms intranet. Neither however is open to the public.
Apertura Designs is promoting JSPWiki as a documentation and collaboration solution for small businesses. They also use JSPWiki exclusively for all in-house project documentation (private access only).
Archaeology Data Service has embeded a JSPWiki engine into its main Java web application to support basic editing of informational pages. See also their "Guides to Good Practice", a resource providing general guidance to the archaeological community.
REALLYREALLYRANDOM - True cryptographic random number generation, with an attached wiki explaining how it's done, the underlying principles and how you might do it yourself.