I've been involve in this industry for more years than I care to confess I can recall upgrading a windows 3.1 environment to windows NT. We went on training courses for weeks to learn how to setup/deploy The UX was such a huge improvement that users accepted it willingly
It's take 20 odd years for MS to risk another major change to the Ui.
I think it's left 2 problems Technologists have to relearn how to do things ( and we don't train now do we!) The advantages of the UI are not immediately obvious (to me anyway)
I like Win 8 , I used google to learn how to do things I used to without thinking. There are things that will need improving . The apps need to become consistent for them once again to become "intuitive"