While I do not use Windows myself for a desktop OS, I can at least understand the reason why people do use it.
What I cannot fathom is why anyone uses it as a server OS. It is truly awful as a server OS.
"Awful" might not be accurate in all cases. I know that it has some good points, and some bad points. I enjoy running "one of each" in my parent company: Two Novell Netware servers, one Windows 2k3 SBS server, and one Linux server.
Novell's eDir simply blows AD outta the water, and is a great platform for email and ZEN. It also makes a great gateway / router since no hackers every try to hack it (shhh... I don't run a firewall, have a DMZ, etc)
Terminal Services / Citrix / VNC / PCAnywhere, on the other hand, is a wonderful thing. I use my W2K3 also is my backup app server.
The Linux world is great for those online duties, and that failover HA solution is definitely on my list of things "to do".
One of the problems that I have with M$ geeks is that they think that M$ has the best solution for every problem. This is annoying, dangerous, and arrogant. Worse yet, no M$ partners dare suggest those alternatives lest they incur the wrath of Oz.
The user interface for desktop Linux is dreadful. The Windows GUI is slightly better, but not enough to justify the additional expense in many cases - expecially with all of Microsoft's security and reliability problems.