I'd say LepriconSoft's UnicornOS is actually Windows 8.1, as strange/infuriating as that's going to sound to many HN readers.
I used Xubuntu or Fedora (dev), Windows 7 (Office), and OS X (XCode) for hours every day for years. I had two self-built machines running Linux, a laptop and a self-built machine running Win 7, and OS X running on a Mac Mini and later a MBA.
Since then, I've also had another desktop and a laptop running Win 7 and Win 8 (though enough coworkers use GDocs now that I've stopped using Windows at all).
Both Linux distros and all OS X versions (from Snow Leopard to Mavericks) have crashed countless times on me. How much they crashed has varied a lot between setups.
Windows hasn't crashed for me (or any of my friends or relatives for whom I'm their IT guy) since Vista came out. It's also never crashed on my old Mac Mini, which is my HTPC setup now.
Whatever you think about the finished products or companies behind them, it's really just a matter of testing and incentives. Windows 8 was tested for 1.2 billion hours before it was released, for example. Microsoft can do things slowly, but when they release something, it has to be rock-solid for their enterprise customers.
OS X, for Apple, isn't a moneymaker and its stability/security obviously isn't much of a priority. They didn't even give it a significant design refresh in years. That's how little they care about it.
The latest version of Ubuntu's desktop edition will ship with at least one head-slapping, show-stopping bug, even though it has a company backing it.
