All our servers are running Debian Etch (except for one that is used for Active Directory and SageCRM) and we have about 14 workstations running it as well. We have been running Debian for about three years.
Our workstations mainly run Evolution and Firefox. All development work is done in VIM. They are all cheap Dells, with about 512MB and AMD 64.
Our servers are running everything from PostgreSQL, OpenLDAP, Postfix, Jabber, Tomcat, and IMAP. Most are just inexpensive Dell pizza rack servers. Our only unscheduled down time has been because the power went out. We run our own APT servers.