I am on Windows 10, Version 1511 (OS Build 10586.456)
It has been very stable thus far, and I am on Windows 10 for that slight gaming performance it adds, specially with the reduced driver overhead that can be seen in certain CPU heavy titles, nothing earth shattering, and if you are on Windows 8.1 there's absolutely no need for you to switch to Windows 10 unless you want to take advantage of DirectX 12. I do enjoy the boost it gets me on certain titles.
It has been very stable thus far, and I am on Windows 10 for that slight gaming performance it adds, specially with the reduced driver overhead that can be seen in certain CPU heavy titles, nothing earth shattering, and if you are on Windows 8.1 there's absolutely no need for you to switch to Windows 10 unless you want to take advantage of DirectX 12. I do enjoy the boost it gets me on certain titles.