I have used WINDOWS SERVER for about 7 years, love it. Whilst many will disagree, it's actually very stable, fast and does the job perfectly. I love that I can log onto the Windows Desktop remotely, and take care of things in an environment I am used to.
Perfomance is not an issue either. I get 200k unique visits a day, every day, mostly during business hours - every visit is database logged, and is powered by .NET. It can sometimes be literally hundreds of visits all running at the same time, everything is nice and zippy, site is responsive and uptime has not failed yet.
I currently use RACKSPACE who offer industry leading support, but you would get away with a much cheaper option if your site was quieter. I also run PHP sites on Windows, with MySQL alongside.
Gary.