I have used Linux exclusively on my personal machines for several years now, but my justification for it is slightly different than yours. It's not about what I can do in GNU/Linux; it's about what I can't do in other operating systems.
Let me explain. I once used Windows exclusively. When I built my first computer in junior high school, my dad bough me a copy of the recently-released Windows XP Professional to go with it. He also gave me a copy of Red Hat Linux 9 and the accompanying (paper-back) user manual that he bought at CompUSA, and he encouraged me to dual-boot. Foolishly, I didn't. I didn't see the point of Linux. To be completely honest, although I considered myself a Windows power user at the time, I didn't really understand Windows that well either. I played with various Linux distributions a few times after that, but it was never more than idle curiosity.
Fast-forward to my freshman year of college. I had started programming in high school, and had become reasonably proficient at C++. As an indirect result, I had learned more about open-source software and started using a lot of it on my machines (Firefox, VLC, MinGW, Notepad++, etc.). Unrelated to my evolving programming skills, I had also become much more adept at fixing problems with Windows. For that reason I was offered a job at my university's IT help desk, which I accepted. One of my coworkers - a man whom I learned a lot from and still have a great deal of respect for - introduced me to Ubuntu. Not only did he introduce me, but he challenged me. Therefore I quickly moved from virtualizing Ubuntu to dual-booting it with Windows on my desktop.
Jump forward another couple years. By the end of my sophomore year of college, I was using Ubuntu far more often than Windows on my desktop. I had reached the point where I only booted into Windows to play games and install security updates. Since I wanted my data available in both operating systems, I still stored the vast majority of it on my primary NTFS partition, which I kept mounted in Ubuntu. I even went so far as to write scripts for programs such as Pidgin and VirtualBox to keep their profiles in sync between the two operating systems. That was a hassle, and there seemed to be no shortage of bugs to be discovered with those scripts. At that point I realized how much of a pain dual-booting really is, so I chose to move all of my important data to Ubuntu and slim down my Windows installation to just games. Since this strategy worked so well on my desktop, I also completely replaced Windows with Ubuntu on my laptop.
The narrative above is missing one key factor: why did I decide to go with Ubuntu over Windows as my main OS? After all, Windows had an obvious advantage: it ran all my games. However Ubuntu had a huge advantage too: a powerful command-line. In the end, the command-line won. I felt like I could do more work faster using the terminal than using functionally-equivalent GUI applications most of the time. I really like the UNIX philosophy. The Advanced Package Tool in particular was one of the most compelling factors of my choice. As time went on, I came to favor the command-line even more. I heavily rely on it in my daily workflow today. The lack thereof remains the number one thing that bothers me when I use Windows. Neither Cygwin nor Powershell cut it (although Cygwin is definitely closer).
Shortly after my decision to use Ubuntu as my primary OS, my Windows installation fell into disrepair. My programming and hiking habits began to eat the free time I used to use to play games. When I did decide to play video games, I played mostly Minecraft, which was really nice because I didn't have to boot into Windows to play it. Booting Windows became a little discouraging because I used it so infrequently that literally every time I booted into it, I had Windows updates waiting to be installed. Therefore I switched to Debian on my desktop (and later my laptop) and completely removed Windows. Although I do not regret the decision to live without Windows in any way, I felt somewhat vindicated when Valve brought Steam to Linux, along with some of my favorite games. I still don't play video games very often, but the growing trend towards releasing cross-platform games virtually eliminates the singular advantage I once awarded to Windows when I was debating switching to Ubuntu.
Although I think that users all-too-often malign the command-line rather than seeking to take full advantage of it, I am far from the only one who sees a good POSIX shell and the traditional UNIX utilities as a huge asset. In fact, Michael Dominick listed it as chief among his reasons for preferring Ubuntu over other operating systems in this week's Coder Radio. As fellow Neowin Linux users, I hope you will agree.