I have not tried the new MSFT Office Ribbon, so I will withhold judgement for now. Others are noting the amount of real estate the ribbon requires.
The only thing I want to point out here is we have gone full circle from ribbons to menus and back. The first GUI applications I developed were CAD tools. Back in the day, those tools were expensive and ran on expensive hardware. One had to go to a special (usually dimly lit) room to use the CAD systems.
Those systems had very expensive, and large, screens. The GUI was essentially an area to present as much of the schematic as possible surrounded by, yes, ribbons. We developers had ongoing discussions to determine how to minimize the ribbon space and maximize the capabilities offered in the ribbons. CAD designers did not want to waste time clicking through all kinds of icons to get to the right function.
Soon after the Mac caught on, then X and Motif. Menus and dialog boxes became the thing. Ask me sometime how this specific transition almost brought down one of the top 3 CAD vendors.