My next system will probably be a Mac primarily running Windows 7 or 8 where I'm currently the most invested. The ability to have both in the same box justifies the extra cost of a Mac to me. My older XP music production system is actually a VMware Fusion virtual machine running on an older MacBook and used mostly for the XP apps.
Both integrate flawlessly on my home network where I use TeamViewer to access them from what is currently my main Windows machine.
Not to say that there is anything wrong with VMWare or Parallels, its just that I happen to like Virtualbox and have used it on Linux and Windows as well.
I was originally planning on getting a used machine but when I looked at the prices of new ones and compared prices, the difference was just too small to take the risks of non-warranty hardware.
That's not the only reason, and perhaps not the primary reason.
My wife made the jump to Mac four years ago. Yes, we bought VMware Fusion so she could run her "must have" Windows apps, too.
Fast forward four years, and she's discovered those "must have" Windows apps aren't "must have" after all. We've found Mac replacements for ALL of them.
No more VMware Fusion. No more Windows.
FWIW: I'm a developer and after being on a Macbook Pro with a Retina display for over a year I can't imagine working on anything else.
Want to buy a song? iTune, 1 click and start listening
Want to install development tool? brew install
Want to install other tools? brew cask install
Want to buy software? App store, 1 click
Want to listen to music on your big ass speaker? Airplay, click and doneEven on Linux, which has arguably the best package repo systems, you still need to go to upstream for important tools because the distros lag behind.
You can get a Mac desktop for $600 and a laptop for $1000-2000, and the prices are going down every year. These aren't cheapo versions of Apple's more expensive offerings, either, they're the real deal, with better hardware design than pretty much any PC laptop. And they run Windows.
How cheap do people expect a computer to be?
Also OSX covers the bases well, both for regular users and developers. One noteworthy group that are left out are the gamers.
Ubuntu? Window of opportunity has passed & Canonical doesn't seem interested in desktop market.
Chrome OS? Awesome as a browser+netbook, but a bit limited for some people's tastes.
Really, if a company like Google had been able to produce a true and full operating system, with Ubuntu/Linux extensibility and the beauty of Mac OS/ChromeOS, they could have come up with a winner ... but it hasn't happened yet.