Can you use Windows in mission critical systems for modern businesses?
If you asked this question yourself then there is very good chance that you are one of people which fall for UNIX worshipper's mutter. There is NO TRUTH in what UNIX worshipper is saying if you don't have somebody to show you the other side of the story and who can question UNIX worshipper's statements and allegations.
Which of the following business you would consider small business? Microsoft, Barnes and Noble, Dell, NASDAQ, GeoTrust, Intel, CDW ...
Well a lot of companies trust UNIX. Does that mean that they are secure? Here is very good example. Major anti-virus company in Russia which trusted their security to UNIX was hacked and all email addresses of their clients stolen. Hackers then sent email to all clients and attached virus to it! It's not just embarassing that UNIX fall but the whole idea of trust to anti-virus company is ruined now. This is not something which can be replaced easily. (Source)
Here is success story about pretty big company (JetBlue airlines) which have chosen to be 100% Microsoft shop (Source).
According to this study majority of UNIX to Linux migrations are not evaluated against TCO and decisions are made by IT personnel just based on acquisition costs alone without taking into considerations other factors.
Here is part of the article
"We found that many times when companies had chosen to migrate from UNIX to Linux, those decisions were made at a much lower level within the organization. In fact, it was often an IT administrator who was making the decisions, typically not using robust ROI (return on investment) or TCO analyses. These IT administrators often put together very rudimentary business cases driven more by personal beliefs and/or “back of envelope” comparisons that would only include something like the cost of the platform, which, as we mentioned earlier, is a fraction of the total cost of a migration."
Look at all those stories, get the facts and make decisions based on facts and not emotions or preachings of UNIX followers.