There was a time when your choice of desktop OS said something about you - you were a Windows nerd or an Apple hipster - hell, Apple even based an entire advertising campaign on it. That was then. This is now.
A couple of years ago I was exclusively a Windows person. I wrote software for the .NET platform, which made Visual Studio my tool of choice, and the software I wrote ran on Windows servers. Even if I was working with VMs, I was running Windows Server VMs inside my Windows desktop OS.
I was always aware of Apple, but as I wasn't a hipster, and had never opened Photoshop, I left them to one side. When I was forced to use OSX I felt quite strongly that it was inferior to Windows.
Then I went to work at a creative agency, where I was swimming in an ocean of Mac-luvin. I started using one on the odd occasions when I need to borrow an office laptop. I still didn't like OSX, but I could get along with it.
At the same time I started playing around with Python, and I decided to scratch an itch I had around my complete lack of understanding of Linux as an OS. So I installed Ubuntu on a VM, and started playing with that.
Then I was given an iPad by work. And I bought myself a Windows 7 phone. So now I had Windows 7, Windows Phone 7, iOS, OSX, and Ubuntu in my life. I even installed Windows 8 when it came out (and paid for the upgrade!), but uninstalled it a week later (you can read about that here).
I finally realised that I had become ambivalent to the OS - and started concentrating on the tools I was using instead. I dropped Visual Studio in favour of Sublime Text, and dropped Word in favour of anything that worked with Markdown (which is anything).
I still don't like OSX - the fact that maximising a window doesn't, you know, maximise it, and the woeful Finder being my pet hates - but I bought myself a MacBook Air as my primary computer simply because I like the hardware, and frankly, I don't really care about the OS.
A beautifully designed piece of hardware running beautifully designed, and simple, software (stand up iA Writer), running on an OS that just gets out of my way, is all I need these days. Are we in the post-OS-as-brand world?
Postscript: the logical conclusion of this is no (discernible) OS at all. Over Christmas I thought I'd be a good son and back up the laptop I bought for my mother a couple of years ago. She uses it infrequently, but enough, and I figured she probably had something of value on it worth saving. In fact there was nothing - at all - on it. Every single thing she does on her computer is web-based. She is the Chrome OS poster child (grandmother).