I took the plunge and upgraded my last and more important PC this weekend, 'cause I don't want to be on the hook to pay $199 for a new Pro license when something forces me off 7.
I swear I'm not a shill; I bitch regularly about Microsoft because my job forces me to bear with it. But I was pleasantly surprised how well the in-place upgrade went. Nothing broke, even my old copy of Office 2003 (from my cold, dead hands...) The only thing the upgrade removed without asking were a couple of 3d-party diagnostic utilities like speccy, which doesn't bother me in the slightest. Even Steam fired back up without a hitch.
Now, about that ugliness. You don't have Aero transparency or rounded edges, but with Classic Shell and WinAero Tweeker, you can do a lot to make 10 more livable. A right-click on the taskbar can make Cortana go away, and ClassicShell separates Windows programs from Metro Apps in separate sub-menus, so you never have to look at them if you don't want to. Also, you do NOT have to use a Microsoft/Outlook cloud account. With this kind of setup, it's pretty much the same Windows as before.
Finally, I haven't tried this yet, but there's Spybot Anti-Beacon to address the "phone-home" issues that might be nagging you.
So, here's an idea to grab Windows 10 while its still free with the least risk. Shop for an SSD upgrade, like a 1TB Samsung Evo because damn it's gotten cheap. Clone your precious Windows 7/8/8.1 drive to the new SSD, remove it, set it aside. Then, perform an in-place upgrade as described here on the clone. Try it out. Something go wrong? Hate it? Swap back your old drive; clone again, do what you like. Your old build is safe and sound.
But here's the thing: according to the article, you have effectively retrieved/reserved your free Windows 10 license to use... whenever. If you want to try again in a few months, you can take a blank SSD and download/build Windows 10 from scratch, Microsoft will recognize your PC signature (assuming you haven't changed you mobo) and license you (just skip the part where it asks for a key). In the mean time, however, your old Windows will still work for as long as you want to keep it.
There. Assuming Microsoft doesn't wimp out and extend the deadline, you've just pocketed a $150-200 license for free to use any time you want.