Installed 8.1 on my surface and my desktop. I have to say this was a really smooth update considering how much was changed. The only difficulties I faced was that it wiped all my logins in IE which isn’t a big problem for me because I keep all my usernames / passwords in keepass but I can see that as being a big thing for other people who click the remember my password and then forget their password.
Another issue I found was with OneNotes send to onenote short cuts. Windows 8.1 has stolen the win+s shortcut for search. It’s understandable and there is a workaround that you can find here http://blogs.office.com/b/microsoft-onenote/archive/2013/06/27/try-windows-8-1-preview-and-bring-back-your-favorite-shortcut-key.aspx hopefully there will be an update soon from onenote to sort it out.
Every other gripe is pretty minor and more or less just about figuring out the new way to do things.