Linux is not Free Software
As an IT Professional, I've had many discussions with my peers about the true cost of implementing Linux in the enterprise or a business environment. The primary argument I keep hearing over and over again is that you don't have to pay to download or use Linux. My personal belief is that someone at some point has to pay for it - be it with money, effort or time. This article from Forbes Magazine outlines some really great benefits of using Microsoft software.
http://www.forbes.com/enterprisetech/2004/08/31/cz_dl_0831msft.html
Thanks to Noah for the article link.