Roskilde University
Roskilde University uses CAS for every web-based campus IT service (currently 40+).
Roskilde has made local modifications to CAS – see this post in the CAS mail archives.
Roskilde is especially proud of their ZESLA: Zero Effort Sso for Ldap'ed Apps, which makes it possible to CASify a webapplication without touching it by writing 10 lines of JSP.