I thought I'd share my experiences with the Win 10 upgrade thus far.
I have a small home network with four computers: two still run windows 7. Two ran Windows 8.1.
I upgraded one laptop from 8.1 to 10, without any problems.
I did do the 'custom' upgrade instead of the express upgrade, and that allowed me to
a) keep all the default programs I was using
b) avoid activating those pesky privacy-robbing 'features'.
The whole process took about 1 and a half hours.
Today I upgraded my main PC, i.e. the one I constantly use.
Again, this was an upgrade from Windows 8.1 to Windows 10.
And again, the upgrade went smoothly, taking the same amount of time as was the case for the laptop.
What is annoying is that apparently none of the settings and data of the Windows 8.1 Metro / Modern Apps (from the Start Screen) are saved.
Each and every one of them gets replaced by a new Windows 10 version, that starts from scratch.
News, Sports, Weather, ... all had to be manually reconfigured.
Worse was that all the 'collections' I had made in the Food App (read recipes etc.) have gone too.
Apparently there are some freeware programs that allow you to keep and/or upgrade some of the old Apps, with their settings.
You may want to install that before upgrading if you have information in your apps that you want to keep.
What is a bit perplexing, too, is that the title bars in all windows now, by default, are white.
The remedy for that is to either use themes, or to use a (freeware) utility like Winaero.
Speaking of themes: none of the Windows 7 / 8.1 themes I had installed seem to work anymore.
I had to manually reactivate the background slideshow, and manually select the folder to choose the images from.
And unlike in Win 7 and 8.1. you can no longer select which images in a folder are shown: in win 10, all are shown.
Apart from that, everything seems to be working fine.
Edge (the new browser) is an oddity. You can't use it to open local HTML files. Well, you can, but it won't read other files it links to: CSS, JavaScript, images... all of which I typically use. So it's useless to open local HTML files.
(And, funnily enough, Edge then offers you the option to open the files in Internet Explorer instead).