We use Debian lenny in our office. We have 7 physical servers and ~10 virtual servers, each of them is running Debian. The servers provide essentially all of the company's services, including (but not limited to) web serving, database serving, IP telephony and IP video surveillance. Also there are about 20 workstations running Debian. We also use Debian on about 70 diskless 'fat clients' to provide access to our web-based accounting and management system.