Everyone's got one.
Windows, like it or not, is an important part of the modern IT landscape. It's developer base is enormous, and there are whack-tonnes of applications extant with no viable open-source alternative.
That said, how your organization treats Windows is entirely up to you. I happen to LIKE active directory as a directory server, so I use it for authenticating all my various machines. I *require* Windows on a limited subset of systems to run mission-critical apps which have no open source alternative.
That said, outside of those, I treat windows entirely as a legacy operating system. We stopped at XP, and have virtualized all our copies of XP used for "office use." The metal boxes under the average user's desk run Linux. We have started the long journey towards replacing exchange, office, and dozens of other applications.
For now, Linux is used primarily as a thin client, RDPing into the Windows XP office boxes, however we are slowly (slowly!) training our staff to use it, and migrating the odd application locally. The goal of course is to have a well-designed PXE "live" launcher that makes the actual hardware under the user's desk irrelevant, and makes for a central change point.
Once we opened up to the possibilities of Linux, (but realizing that Windows was critical, and had to be maintained in certain environments,) there was this whole other world of ease-of-administration available to us.
Other companies have different approaches. The fact that we have the choice is waht is excellent. Any choice except a Mac is one I respect, as long as it is administered properly.
Flames because Administering Macs in a business environment makes me irritated, and I thusly like to inflame the Mac fanbois.