I hope you mean as a client OS.

On the server side of things, Linux is the fastest growing OS. IBM, Compaq and HP are throwing considerable weight behind Linux.

Movies like Shrek are rendered on Linux boxes. Check the statistics for web servers on the internet. Linux is big time right now.

At the moment, Windows is unbeatable on the client side and you are right to develop exclusively for it.

As far as having to enter a password, ever use NT or 2000? Linux can be configured to be just as insecure as Windows9x is out of the box.

Check out the costs of getting an MSCE and keeping them current.

Check the cost of licensing for MS products. MS makes decent stuff and they deserve compensation.

I as a consumer can see that I can solve 80% of my technology problems for free. Huh, guess what I'm going to do?

MS has good stuff. Linux has good stuff. There's no shame in using both.