Note, I have installed multiple distros (Gentoo, Mandrake) in the past, and enjoyed the challenge and learning experience. I use whatever I need to use to get the job done, so I am no fanboy, of ANYTHING. Then again, you could say I am an Anti-Fanboy..
That is sometimes the case. I think that for a lot of linux users, we prefer the power and flexibility you get with Linux. Sometimes all of the various options are bewildering to newbies, but for us, it means we can choose exactly the right tool for the job.
In the case of some, like mine for instance, my loathing for anything microsoft comes from having been forced to deal with their twisted concepts of computing for so many years. (rebooting to change network settings?) I can't tell you how many months of my life were wasted spent troubleshooting software that never performed as advertized. These days, I don't admit to knowing anything at all about windows systems, so I don't have to support them. My mom was complaining about her stuff not working, and her computer constantly being infected with viruses, worms, and crap, so I toasted her box, installed Fedora, built her a few user accounts for everyone, and then left. Since then, she hasn't made so much as a single support call. Her email works, she can browse the web, she has a word processor, and her geneology program right on her desktop, so she can always instantly go to anything she needs.
Unlike a lot of the bashing you hear of Linux and OSX from windows users who have never used either to any gret degree, my hatred of microsoft is honestly earned, and not just speaking out of ignorance.