Not retired, but I do a bit of in-home support for people in my area. (Most of them are older users - I used to work in the IT department of the local retirement home.) I've had a few that unintentionally upgraded that I helped roll back, one that I had to reload Win7 since he waited more than 30 days to decide he didn't like 10.
I got a lot of calls from people asking about the upgrade. Most of them decided to stay with Window 7 after I told them that 7 would be supported until 2020 - they figured they'd be getting a new computer before then. (Several of my elderly users half-joked about whether they'd still be around by then.) I had several that moved from Windows 8 to 10 and thought it was a big improvement. I didn't have any Linux conversions because of Windows 10, but years ago I had one because of Vista. He was a happy Ubuntu user for a couple of years, then switched to a Mac.
As for my personal experience, I upgraded my laptop shortly after 10 released, partly to see how it would perform on older hardware. Turns out that Windows 10 is painful on a Core2 Duo with 2GB RAM, but no more so than Windows 7. I upgraded my desktops within the last week of the free upgrade. The only problem I've found so far is that Infrarecorder - an Open-Source CD/DVD burning program - won't run. The splash screen flashes up briefly, then nothing. I've only tested this on one of my desktops, and this was a pretty well-worn, crufty machine that was my daily driver for years. Haven't tried it on another machine yet, so it may be a fluke.