I used to have a dual boot setup for ages, finally switching over to Linux as my main OS with a Gentoo 1.4 RC.
Back then, still being a cheapskate student, I really became a Linux enthusiast, one of those fanatics who literally spent hours in forums after having the gcc manuals for perusal every night to squeeze out the last percent of performance with custom linespanning make arguments. On the GUI side I had KDE (3.x was a real charm at the time!) and Fluxbox and used what seemed the better fit for the day. At that time with my Gentoo stage1 build set up and other fun things like my OpenBSD-powered home router on an old Pentium PC, you would have never convinced me I would ever churn from FOSS. It was also then I gained the invaluable knowledge that helped me great deal to get my first job. Good times.
Fast forward a few years. I'm sitting most of my daytime in front of computers now, in my office and in the afternoon. Tweaking configs and waiting for builds to complete was not the exciting pastime anymore, it became simply hassle. So I went from Gentoo to Kubuntu. I never liked *buntu-based Distros as much as Gentoo, so M$ had me in a weak moment.
Windows 7 with its 30-day-trial was too tempting, and it simply worked. It was sleek. It brought great improvements. And I went to the store and bought it. (Fun fact: the /. quote of the day below my input box right now is "We are Microsoft. Unix is irrelevant. Openness is futile. Prepare to be assimilated.")
Today I'm still sticking with Windows 7 as my only OS on both my desktop and laptop. Linux distros only reside hibernating inside VMs for me to tinker around with sometimes.
Sometimes I ponder whether I should go back, as I'm afraid I'm narrowing down my own IT skills with the way I use computers nowadays. But, to summarize my excessive storrytelling, you have to want to invest time and effort into Linux. And after some life advances I just don't want to invest the time. Windows is as easy to use as ever and it got rid of the better part of its design flaws and downsides.
However, there's still that Debian powered server running ownCloud and some other stuff keeping me attached to Linux. And, of course and without much notice, my Android powered phones.