-Windows for games and Active Directory-managed MSOffice-dominated corporate offices.
-Mac OS X for creative types and the content creators for the aforementioned corporate offices.
-Linux for the sysadmin to play with at home and, at work, to have running on an old box in the server room to do a task that a Windows server could probably do just fine, but not as efficiently, and is in constant danger of being replaced with a Windows system, just so the SOX manager will be happy.