The ribbon interface makes users less productive than ever before. It requires more time and mouse clicks to do the same operations than in previous versions, despite the propoganda put out by PTC. The ribbon UI also eliminates the opportunity for users to utilize the innate human ability to spacially recognize objects. Limited customization options and poor use of screen space compound the issue. Leave bad UI implementation to Microsoft, do your own useability research and build a UI that works specifically for CAD users.
Above all, remove the ribbon from future releases of Creo.