The shortcut keys from older versions of Excel still work. The new ones are easy to find too (hit Alt and they appear, but you can type ahead full speed)
One really positive thing about the Ribbon was that it exposed every command in a Microsoft Office program to a keyboard shortcut. Yes, in earlier versions, most had a keyboard shortcut, but some commands only appeared in toolbars that only showed in certain situations and were never mapped to a keyboard stroke. Now in the ribbon, every button that you can see has a keyboard shortcut.
