Mur.at - Verein zur Förderung von Netzwerkkunst, Graz, Austria
We use Debian on various servers as well as on our desktop machines, laptops, and routers. We use postfix, dovecot, openldap, apache, bind, kvm, postgres, and mysql.
Debian has proven to be a reliable Operating System for our network over the past 15 years and we especially like the social contract that guarantees that Debian will stay free software.