At this point, if people don't have an absolute need to run Windows, I do my best to get them using something else. I'm referring to the (too many) people that I have somehow found myself responsible for providing computer related services to.
If you're not a gamer, or have some professional need to use a particular piece of Windows software, there's nothing to gain from continuing to use it. Here is why.
DISCLAIMER: These points are relative to other modern desktop operating systems, not previous versions of Windows. All versions of Windows share these traits to some extent, improvements as well as regressions have been made over the years/decades.
-It's not easy to use, that's just a matter of familiarity. Other desktop (and mobile) UIs have advanced far beyond it in terms of consistency and usability.
-It's a bloody security nightmare, always has been (at least as long as it's been connected to the Internet) and as far as I can tell always will be. The process for applying updates/patches is arcane by modern standards. It's a patchwork of separate procedures for Windows itself, and all the various software that it runs, if a program even has a function to update itself short of redownloading a new version of some .exe file from the authors website. (Seriously, what the hell kind of gong show is that?)
-It's slow, and performance degrades over the life of an install. People compensate for this shitty performance by throwing stupid amounts of computing power at it, wasting money and electricity. Fixing this by doing a fresh install is extra painful because of the total lack of standardization for things like location of user data, making saving/restoring it a real hit and miss experience most people would rather do without. Not to mention the process of gathering hardware drivers just to get it up and running again. Ever install Windows to find your network adapter isn't supported out of the box, because almost none are? Show stopper until you get those drivers on a USB stick or something so that you can continue downloading more .exe files from more websites to get the rest of your hardware working. A decent OS (all of them except Windows) will support most common hardware without additional drivers.
-It's just not necessary to run that much code on your computer to get things done anymore. What most people these days need is a good platform to run a full featured Web Browser well (i.e. Firefox or Chrome, not whatever hunk of crap MS includes). That's where the magic happens nowadays. People need their GMail, youtube, facebook, etc to work. All web apps. Windows is about the least suitable platform for this. I mean seriously it's like 20GB+ of code after fresh install, to do what exactly? A modern Linux desktop install is like 1/4 that size, and actually includes some real functionality. Chrome OS is a couple of GB, the Android I just installed on my phone was under 500MB.