Windows 8.1 has better overall performance, faster boot especially on uefi gpt ssd, vastly improved ssd handling with more aggressive trim functions, storage spaces and support for ReFS, better memory management, much reduced install size which is especially nice for 2**GB or smaller SSD instals which can be made super tiny with WIMboot, onedrive account sync which is super nice for those that have multiple computers as all your profile setting are there on every machine... and believe it or not, some of the metro apps are actually pretty nice even on a desktop.
Ribbon interface is nice now that I have become accustomed to it. I'm a big fan of the default theme on 8.x and it's the first Windows version I haven't felt compelled to resource hack and mod extensively. Copy/move dialogs are much more informative, much better task manager with more detailed information
I really like 8.1 and it makes 7 feel really old to me now. I really like the start screen much better than the old start menu. If you take some time to organize things into logical program groups, and create some additional shortcuts in them for things that don't come up on search (like programs that do not require installation) it makes finding things easier. I like seeing everything at once, and not have to click though layers of stupid nesting on the old style menu. I also like live tiles but think they are currently way under utilized. I wish more programs took advantage of them to show things like when updates are available instead of running crap in the tray.
Search is also much improved as hitting the Windows key and start typing not only shows applications but user files too. It really makes no difference if it comes up full screen, as on the old way it would be in focus as well... once you start the application it goes away so I can't see how it is any kind of hindrance.
