I did the upgrade to Windows 10 in August 2015. I thought I was having problems with it, turns out it was a problem with my laptop battery to laptop syncing.
I have had no problems with Windows 10 itself, I did have to re-install a driver for one program I run after the Windows 10 switch.
It works very well for me. In my area, the upgrade is free until sometime in July 2016. After that there will be a charge but I don't know what that will be.
My tech support guy did tell me that there will be limited support for Window 7 or 8 on an ongoing basis and it will be discontinued entirely once Microsoft is sure the bugs are out of 10.