Just some notes from my experience of Windows 8.1 upgrade.
1. It's slow to install. Like I'm sure it took longer than the initial install of Windows 8!
2. Start button is a have. Just goes to Metro. It's Metro I'm not a fan of, which is odd given I spend most of my time in Gnome 3 and I use metro in the same way. Press windows key and start typing. Metro is just to busy.
3. App problems. I was going to say none but VMWare player had to be repaired as the networking bridging sopped worked. I showed the interface as down and the bridge interface list was empty. After being repaired it was fine..