The other issue is of a huge concern and generally a huge PITA for users and that can all be described in a simple, very well worn statement...

"Change is inevitable... change for the better is not".

My favorite example is the "Ribbon Bar" in Microsoft Office.  Such a thing was a great idea but it now takes many more (totally unnecessary) clicks to do many common tasks never mind actually finding the correct ribbon to use for a task because certain functionality actually seems to be on the wrong ribbon.