I burned up five Win 8 Pro upgrade pre-order key codes that I bought but never installed in the past couple of weeks to clean install it on a small herd of old machines. Everything works, but the installer and Win 10 could not find a driver for the graphics card on the oldest machine. Fixed that with a Vista beta from the manufacturer.
My niece was over yesterday, and had never heard of the upgrade offer (does mostly cell phone browsing and email) and wanted me to help her upgrade her Win 8.0 laptop which apparently had not seen Windows update for a month of Sundays. To begin, although she had no less than five antivirus programs installed, she managed to collect a couple of dozen infected files. Then we started trying to get to 8.1---147 updates that took well over 5 hours to locate and download on my high speed connection. I assume that the update servers were taking a pounding. Trying to use the automated get Windows 10\update this computer now resulted in another several hours of slow activity but no success. By then I was getting worried about the deadline. I used a usb drive on which I had the installer already, but made the mistake of clicking the check for updates button during installation and the install went into checking for updates for several more hours. Cancelling the install left me watching the clean up screen for another hour and a half before I gave up. Finally I forced a reboot, and started again from the USB drive skipping the check for updates and everything went fine. Finished a good 22 hours before the midnight UTC 10 deadline with an activated Win 10 installation and her files intact except for the ones caught by the virus scan. Anyone who has not done this by now is probably SOL. Definitely use the media creation tool to make a USB drive and run it from there.