We are running Debian for several applications both in-house and deployed at customer sites. We use it for web and email service, Cacti and MRTG graphing and to run Asterisk PBX. We also use it as a base for SNMP monitoring, network asset collection and trouble ticket systems.
We have Debian deployed on approximately 50 servers both in house and at customer locations, serving all of these applications. We continue to use Debian in environments when we need a reliable server environment for a purpose-built task.
Debian has proven to be extremely reliable and we will continue to use and support Debian.