University of Rennes1 uses CAS, mainly for uPortal (thanks to Yale cas-client patched to use direct URLs to channels), IMP (patched with phpCAS), cyrus-imap (thanks to pam_cas), SunOne Calendar and other minor applications.
Technical contacts:
Using CAS 2.0 functionality.
25,000 students and 3,000 staff people.
Perhaps should mention the rather detailed doc:
http://perso.univ-rennes1.fr/pascal.aubry/presentations/cas-eunis2004/index.php