My Surface Pro 3 upgraded flawlessly. Since upgrading my Surface Pro 3, I have seen longer battery life, near instant wake up times. Better tablet mode. Better desktop mode.
My Lenovo W530 also upgraded just fine, though it isn't a tablet or touchscreen. I still like the experience better than Windows 8.1. Unfortunately, I cannot create a new user and login. I can only use the one user that already exists. I put an hour into fixed this and couldn't. The suggestion is to copy the c:\users\default folder from another windows 10 computer. I haven't tried that yet.
Two of my devices failed to upgrade. One entered a boot loop and I had to boot off a Windows 10 install CD, go to repair and troubleshooting and recover it all myself from the command line. Not something the average user could do. The forums said to reformat and there wasn't a fix. I managed to put it back together without a reinstall and it is back to Windows 7. The issue were never resolved before the final date for the free upgrade came and went. Not sure if Microsoft will let me upgrade now. I have an MSDN subscription, so I don't necessarily need the free keys, but I would like my personal devices and their keys separate from my work's MSDN keys.