I ran the upgrade today, and thought i'd share my experience here.
1. I actually did not mean to run the whole upgrade today. I thought I would get a prompt to either upgrade this PC now, or to create upgrade media, and I was going to download the .iso first and burn it to DVD. I guess there is some other sort of download tool I should have used for that, though. It said it was preparing my PC, so I thought maybe it was installing some final compatibility updates or something. But once I saw "windows is updating; do not turn off your PC" I decided to let it run its course.
2. The upgrade process itself went fairly smoothly and was hands-off. At one point I saw that after a restart it was "attempting to recover the installation", which it did successfully. I didn't time it, but the whole process took aver half an hour.
3. When it was all done, the screen asked me if I was Michael (I am), and I clicked yes. I did not sign in with my Microsoft account. Windows 10 desktop appeared, but it was not my old desktop background or theme, and most of my desktop icons were missing. Going through the personalization menu, I could not find any of my themes I had created before. I tried opening something (I don't remember what), and UAC popped up asking for an administrator password. Oh, hail, no! Not on my account. Wait, is this my account? No, it had booted into my daughter's password-restricted account! It took me a few minutes to figure out how to log out of that and log into my account. There were my icons, background, etc.! UAC was still enabled so I shut that nonsense off again.
4. Edge did not automatically import my favorites, settings, and homepage tabs from IE. Yes, I prefer IE to other bowsers; don't hate. I found the option to import favorites from IE or Chrome, but it did not list Firefox, which is also installed.
5. IE11 is also installed under Windows 10, but it seems to run very slowly.
6. The only program I have had to reinstall do far was my Logitech Gaming Software for my G700s mouse. Oh, and I had to uninstall Trend Micro's RUBotted beta software before I could upgrade.
6a. I had no sound but did not realize it until several hours later. Device manager showed all OK, nothing was muted, and all wires connected. But the Realtek software said I had no speakers, and the windows sound configuration would not play test tones because the device was unsupported. I reinstalled the driver using the one form Realtek's site. It uninstalled the old one, but said the new install failed. I tried anyway, and the sound is working now, but I no longer have the realtek software that I rarely used anyway. I'll investigate further in the morning.
7. I have tried only one game so far - a quick skirmish on C&C3: Kane's Wrath expansion. It ran flawlessly.
I plan on posting further updates as I discover new issues, etc. I just wanted to get down some initial thoughts while they were fresh in my mind.
I also plan on doing a clean install soon-ish, on a formatted SSD. I'm just dreading reinstalling all my programs, but windows 7 was starting to flake out on me even before the upgrade, and I am not sure if it was an issue with windows, drivers, undetected malware, some other software, or hardware. I know my SSD has "dirty bit" set, but it would always hang when I ran diskcheck, so I disabled diskcheck for that drive. I'm hoping a reformat will clear that up. My PC has been randomly hibernating (even while I am typing) and locking up (but no BSOD), so I wonder if it related to the dirty bit.
EDIT: Added 6a.