London Health Sciences Centre, Ontario, Canada
We use Debian Linux servers for all of our Linux based servers that don't have commercial vendor requirements. Including but not limited to web servers, DNS servers, DHCP servers, Samba file servers and java application servers.
The reason we use Debian over competing Linux distributions is due to the high quality of the Debian operating system, the speed in which Debian releases security updates and the freedom to not have to manage software licenses on our Linux servers. With commercial distributions we find we spend more time managing licenses than managing servers.