Wow, I've never actually run into someone who uses ARM seriously. Didn't realize it was actually viable considering that you're basically stuck if you ever happen to need anything proprietary, because nobody really touches that kind of stuff for non-x86 platforms.
I just run bog standard x86 hardware. It's easy and widely supported. I run quite a variety of OSes based on needs... I sometimes feel like I don't have a home.
I use Windows on my most powerful box because it was built for gaming, and obviously you're not going to find games anywhere else. I find myself doing a lot of work on it, too-- just feels right and when it comes to special, specific-use software Windows is typically where you're going to find it. However, I find it to be rather heavy and out of my control, even after lots of tweaking. It's also only customizable up to a point, which sucks when you want to try putting together a consistent look and feel.
I also have a MacBook and obviously run OS X on it. This made sense at the time I bought it, as I was working on graphics/artsy stuff. Also Mac hardware just seems to have the superior notebook experience-- great battery life, decent weight, and a superb trackpad. While I always really like OS X when I start using it for the first time after a while (dating back to the PowerPC days when I would use friends' machines) I find that the longer I use it at a time... the more I dislike it. Things just seem way too big and the UI doesn't give me the right feedback (wish I could describe that better). Finder is junk when trying to manage large amounts of files. I also have trouble finding software for specialty tasks sometimes. On the other hand I like its implementation of virtual workspaces, full screen apps, and window management-- and how it ties into the trackpad's multitouch gestures. However, the notebook experience is decent enough that I keep using it as opposed to selling it off. Although, if they got the discrete/integrated GPU switching to work on Windows (thus keeping the battery life acceptable), I would probably just install Boot Camp and stay there.
I also use Linux, though mostly as a hobby for now. In the long run, I would like to switch entirely to it. I absolutely adore the deep level of control I have over the system, the vast customization and choices of desktop environments/window managers, and cool tricks I can pull off. I love how in certain distros I can pick EXACTLY what I need and nothing more. It's true efficiency. I do feel it's better at having specialty stuff than OS X, but not as good as Windows in that way-- and they're mostly command line so that kinda sucks unless you take the time to script things out (though once you do that, it's awesome). On the other hand, it's annoying that you pretty much have to depend on your distro's packaging system or compile stuff to get it to work-- you can't just drop binaries around as much like on Windows. Could be annoying if you ever want to use an older piece of software for some reason (could see this applying to games for instance). On Windows that's easy, but on Linux not so much. You're pretty much stuck with whatever is current unless you run an ancient distro, but then of course you don't get current software. You can't mix and match.
I guess overall that makes me a Windows guy... I get the most useful work done with it right now. You really just can't beat something that widely supported.
