I had to leave my SP3 at the MSFT Store, and they said it won't be ready for about 3 days. They are really backed up rolling back lots of PC's to Win 8.1 apparently. Why am I not surprised. They were touting Windows 10 so much at the press conference, but it's just not ready. Too many bugs, especially with Cortana. Believe me, I want it to work, but I'm not going to attempt another upgrade for a while.
Upgraded my girlfriend's laptop to Windows 10 but it killed the Wi-Fi. Obviously spent some time on Google and there were many others with the same problem... it seems related to upgrading whilst a VPN is installed/in use.
Tried some fixes I found such as device management configuration and changes to the registry... but nothing worked she needed it back and working for the following morning so back to Windows 7 it was! Slightly disappointing really.