Departamento de Arquitectura y Tecnología de Sistemas Informáticos (Facultad de Informática), Universidad Politécnica de Madrid, Madrid, Spain
We use Debian GNU/Linux on our servers and workstations. We have one main server with the following services active: NFS, NIS, CVS, Subversion, Git, Apache, FTP, DNS, POP, IMAP, SMTP.
Regarding the Workstations, we have around 15 machines using Debian with different desktop configurations (mainly KDE and GNOME). The software running on those systems varies, but they are mainly used for scientific and research purposes, so you will always find: LaTeX, GCC/G++ Compiler suits, GDB, Python, Octave, etc.
The main reasons for selecting Debian and not other distributions are the effort on providing good quality free software and its ease to administer the installed packages and configurations.