May as well throw in my two cents. The government office I work in, which is supporting one of the largest Departments of the US government and probably the second largest Agency within that Dept., uses RedHat when they choose Linux. We have DNS and DHCP for at least 60,000 users running RHEL. We run web servers and Tomcat application servers on it. I believe that some Windows 2003 and 2008 Servers run in VMware instances on top of RHEL. I don't support that stuff, so it's a bit of a mystery. I do support RedHat mail servers as dedicated machines for sending fingerprint data to the FBI.
We have a mixed environment here, RedHat, Windows 2003 and 2008, Mainframe, System 36, AS400, Active Directory and Windows XP on desktop. Most places are some kind of mix as services are added over time. Use what works, use what you can get a support contract for if it matters that the server is down. If you have an SLA, cover your ass.
Brian Kelsay Sr. IT Specialist/Systems Analyst Anadarko Industries, LLC, working for: USDA/OCIO/ITS/TSD Kansas City Large Office Phone: 816-926-6897 Fax: 816-448-5605 Email: brian.kelsay@kcc.usda.gov