What about privacy?

I hate to be "that guy". The one putting the tinfoil hat on every few minutes, the one warning everyone of privacy issues, the one spouting online about it every few minutes.
Truth be told, I'd much rather steer clear of all of it, we all know it's there, and it all comes down to politics and personal agendas. Those are no fun to deal with.

But, we are living in a post-Edward Snowden world, and I'm sure someone will complain to me if I don't mention it (as they have in the past), so here we go!

To make a long story short, there are many privacy violations present in Windows 10. Two which readily come to mind are the presence of a keylogger "for debugging purposes", which may or may not have been removed from the "final release", and the fact that the new Cortana feature is supposedly always listening to you. I'll refrain from talking about Cortana, as I have no real experience with it.

The term "final release" is very vague here, as it is unclear what exactly the "final release" of Windows 10 even is. There seem to be two branches, "stable" and "insider preview", both of which are readily available to the public (although the latter requires a Microsoft account and a few other things). The presence of the "insider preview" and its continued development suggests that really there IS no final release of Windows 10.
Further complicating matters is the fact that Windows 10 is to be the last release of Windows, per speculation around the internet. Some of the speculation surrounding this holds merit. Which means that there could really be no final release of Windows 10, well, at least not until Microsoft goes out of business, but how likely is that?

Above is a screenshot of the "privacy" applet in the settings Metro application. I strongly suggest going through this with a fine-toothed comb and turning alot of it off. Even this may not be enough, there's an awful lot of privacy-related holes in Windows 10. Again, I'm not getting into all of them, because I don't find "tinfoil hattery" to be a fun proposition, or my idea of a good time.

The really nasty thing with all of this is some of the "forced upgrading" shenanigans Microsoft has tried. There is a Windows update, KB3035583, that when installs, provides the user with a "GWX" application, which stands for "Get Windows 10" (or, perhaps, "Get Windows X", in yet another ripoff of Mac OS X). This application is notoriously persistent, and screws around with Windows Update, as well as popping up dialog boxes begging you to upgrade to Windows 10 "for free".
Nothing is free in this world. Windows 10 is a privacy nightmare, you'll be losing quite a bit of anonymity on the internet (or at least to Microsoft, who may well turn around and sell that information to "advertisers"). Many people have been tricked into installing Windows 10 upgrades who didn't even want it. Worse yet, the "downgrade" process is buggy and doesn't work correctly if even at all. Sounds like shady business to me.

Speaking of shady business, Microsoft has also passed some of the telemetry features down to older versions of Windows. Not to mention that various updates relating to telemetry and Windows 10 upgrades reappear just about every Patch Tuesday despite already being hidden.

A (non-comprehensive, maybe) list of Windows 7 updates to avoid is located here.

I'm really sorry to say, but I refuse to allow Windows 10 on any of my personal computers. I have exactly one system running it so I can remain familiar with the interface, and that's it. I refuse to let my computer be used as a vehicle to further a Microsoft employee's personal agenda.
I don't care what you think of Windows 10, in my experience, it has been a buggy piece of garbage that has numerous privacy holes in it. I've had people tell me in the past "well, it works fine for me!", to which I reply, "good for you". I'm really sick and tired of hearing all the M$ shilling going on.