Recently read this white paper. Worth reading..

Below are some excerpts..

Almost 95% of the servers at Microsoft Hotmail run Apache web servers on FreeBSD UNIX, according to Netcraft, while MSN runs on Solaris and Microsoft LinkExchange runs entirely on Apache/FreeBSD. Microsoft themselves appear to understand that it is not worthwhile to run their very own operating systems or web server software, after spending almost four years on the task of shifting to Windows NT (then 2000) and fifteen months after the first load balancing machines began to be shifted from FreeBSD. As the web site The Register has noted, more of Microsoft's FreeBSD servers just seem to pop up again and again. When confronted with public whimsey at evidence of their UNIX and Open Source software usage, Microsoft installed "interceptor" servers that prevent identification of these non-Microsoft machines from being displayed, as in the redirect of queries of LinkExchange servers to Microsoft's BCentral site. In February of 2002, IT industry watchers were amused to find that a web site run by Microsoft and Unisys to tout the "benefits" of Windows OSes over UNIX was, in fact, being operated on a UNIX server. It should also be noted that such Windows "booster" sites as Windows eXchange, WinOSCentral, and most PC hardware sites use the Open Source Apache web server on Linux or *BSD UNIX rather than Microsoft products.