Windows 10 UpgradeAll right, since I'm sure some of you are doing this at some point in the next three days (while it's still free), here's a quick summary of my experience.
1. Clean up your crap
I consolidated everything I could, deleted everything I should have deleted two years ago, and uninstalled apps that I should never have installed in the first place.
2. Backup your important stuff
Probably, it will be fine. If it's important to you, though, put it on Dropbox or somewhere, just to have a copy if the upgrade goes sideways.
3. Microsoft can be startlingly inept at times
When you start downloading the update, depending on how you choose to do it, you may not have any information on how much of the download has completed. And when it's finished and you try to install, you might get this "preparing to install" message for--in my case--about 8 hours. With absolutely no additional information about what the hell was going on. So don't expect any clarity during the download/preparation steps. It's embarrassing, really.
4. Microsoft can also be startlingly competent at times.
However, once the actual upgrade process started--with an actual percentage complete indicator--the entire upgrade was very quick and utterly competent. No device issues (although I recommend unplugging everything you can, like a printer, and adding it after the upgrade is done). No program issues. It appears to be a very, very clean upgrade.
I've used Windows 10 on my Surface Pro 3, and the way I use it is that I never go anywhere but the desktop. I don't go to whatever the hell Microsoft calls the multi-panel UI, because I can't imagine anyone ever producing anything in that environment. It's fine for being entertained, but I want to produce things, too.
The upgrade didn't start me out on the garbage panel. I don't even know if that panels exists, because all I've seen is the desktop with my familiar screensaver and my desktop icons, which didn't move at all (that drives me nuts). Totally familiar and comfortable.
5. Privacy is seriously messed up.
You need to read this (thanks, Theo) to understand how nefarious some of the default settings for privacy are in Windows 10: Broken Windows Theory. It will take 10-15 minutes to change all the privacy settings for the better, but it's well worth it.
6. Windows 10 is sleek, fast, and very easy to use.
I was a big fan of Windows 7, but this is better. It's slick and very fast.
Do I have any complaints, now that the upgrade is complete? Not one.