We are using Debian on 2 of our main Proxmox based virtual servers, which run and support an additional 6 Debian based servers.
We also run a desktop installation in our company for our admin, and a "bare metal" server for backup, local DNS, and file sharing. The server is also used by our web designers for testing new websites and web based applications.
We use Apache, Nginx, Exim, Mysql and Samba, with support for PHP, ruby and python. We have an additional server for testing of new configurations and benchmarking.
Debian is our main server system because it's stable, has a good community and a large volume of available documentation online.