I upgraded 5 computers to Windows 10. Two were basically empty computers that did not have much data. My final upgrade was my own personal laptop with all my programs and data.
On each computer the upgrade was smooth. It took between 1-1/2 to 3 hours depending on the computer. I was greeted by the new login screen and desktop following.
I thought to myself, Microsoft has done it! They actually made a working upgrade that was painless! However, my excitement was short lived. I began using my personal laptop and found some issues.
Autocad 2016 has display issues. Some games will not recognize user input. And I found other sundry issues. Hopefully everything will be patched soon. However, if you have important programs on your computer, check to make sure they work fine before you upgrade.
BOTTOM LINE: the upgrade goes smooth, but be prepared for unexpected program behavior.