I upgraded both my desktop and laptop, with the former being done through Windows Update and the latter through the Upgrade Assistant (I didn't want to wait). Other than an issue of having no Windows startup or shutdown sound, and having an issue with notifications, I didn't have any issues to speak of. No missing files or folders. The notification issue was that the popup would occur on the bottom right, but when I would click on the notifications icon on the bottom right, nothing would be there.
Still, due to the issues, I decided to go back. Luckily, I'm one of the folks who saves a system image before any major updates or upgrades, so going back was relatively easy. I don't trust the rollback feature. So, I restored both with the system images and all is well.
When it is released again I am going to download it using the Media Creation Tool, burn the ISO to a DVD, and upgrade both using that. I'm on a capped ISP, so doing that will help me save data over upgrading each one through Windows Update. And, of course, I'll be saving a system image from each before upgrading them. Everyone should. It can save you from a major headache.
I'll be waiting...