Debian is used as a central server which handles e-mail (fetchmail, Exim, popa3d), which displays intranet pages (Apache), and which provides access to the world wide web (Squid, BIND). We extensively use Perl for the development of AccessControlSystem, to compute and analyze telephone calls made from the company. We use programs to compute production dispositions and display them on the local intranet.
We use Debian because its software quality is best of all distributions. Even if we have to wait a year or two for upgrades to the newest versions, we are sure everything will work fine.