I think that there are actually very few Windows fanboys. The only true ones are the ones who work in IT or with Windows computers for a living in some way. The others who claim to be so are only doing it because they dislike Apple. They also tend to use Linux at the same time, so they can't really be considered fanboys.
Apple fanboys are the worst by far. They get overexcited about their computers, they're egoistic, they'll just show off stupid flashy features on their Mac and use the "no viruses" argument over and over. Honestly, they're just computers. Each OS has its merits and its faults. I like all three, but I use two (Windows & Mac OS X). I don't discriminate. 🙂