I recently took the plunge on my primary workstation and clicked the Upgrade to Windows 10. I have been using Windows 10 on a Surface Pro 3 for over a year, but had delayed switching throughout the office. I had been using Windows 8.1 with Classic Start Menu enabled.
Apart from the hour it took for the PC to process the upgrade, there was very little I had to do. Of course, my Classic Start Menu was disabled, but then again Windows 10 essentially restored the Classic Start Menu found in Windows 7, and then threw some tiles on as an option. But what was surprising was that the computer seems to be “zippier”. I believe it is ultimately a programming trick, but programs load and start faster.