I'm one of those who has 10 working OK after messing and tweaking for a week..........
I have 1 external HD, 2 USB sticks, a USB keyboard and a USB mouse connected to this HP laptop, matter fact everything was connected while I was doing the update, I did do the upgrade via the full ISO download though and the setup burned to DVD along with a USB installer too. I had some problems with my browsers at first too, but they corrected on FF and IE after using Chrome on a few sites that would open. I had some games that didn't want to work, found going to the folder using file explorer and clicking the exe did work, have since re pasted the exe to my game folder. the only other thing was my security suite, COMODO, they released a "fix" yesterday and now that's running fine again.
Have re done some GUI stuff for my own taste ie the W10 desktop, and took ownership of the usual folders that won't let you in. Have had no other issues every other program that was carried over is working on 10 as it was on 8.1, incl all 32bit stuff.
One thing I always do is make a "FULL IMAGE" of my current system before i do anything that entails drastic changes or large updates/upgrades, so I can always go back to a prior setup. If you had/have made a USB boot stick and had done an Image even with the built in W7 imaging , you could already have recovered your system, as it doesn't need to boot into windows, the USB stick is your bootable media, and from there select the USB drive that has your Image to recover. I use 2 separate Imaging programs, the built in W7, and AOMEI Backuppe, both have been used to recover and work well. matter fact I had to use the boot stick and the Image I made of W10 just 24 hrs after installing 10 cause i hosed up the network trying to uninstall/reinstall this COMODO suite, the Image got me back to where I was with 10 with no problem. I learned the hard way years ago when I lost my full drive and had to spend 36 hrs straight re doing my system, never want to experience that again.
So yeah, there are some that have the monster tamed lolol
In my case though I never leave well enough alone, I'm constantly installing software and tweaking my system one way or another esp with graphics, I can't help it
Good luck to the rest of you, I'm sure it will work out, I remember well how much fun W8 was when it first hit the street