Keep in mind that these are random grumbles and not a methodical critique--
Top keyboard grudge in ribbon-land is that the UI no longer helps you learn keyboard paths. Until this change, you could tell any Office app to put underscores on menu commands so you know how to hit them with the keyboard. Some unknown but large chunk of my former speed was not that I remembered exactly how to get to some less-used feature or even how to do a complicated thing regularly without looking at the screen.
Right close behind that is the loss of customization. I don't have the volume of same-type documents pass through my hands that I did back when Office XP was in beta, but I still get piles of things with repetitive task requirements that I could push through more quickly if I could just build a little toolbar and give it the keyboard commands I wanted.
Being able to customize 'properly' would also be a big help for me in the general process of copy editing, which often includes cleaning up great piles of paste-dung left behind by folks who have no idea what the Paste Options button is for. Previously, I could use the Standard toolbar to keep an eye on the style and font info without having to mouse around for that ghostly minitoolbar. When I started stepping through tracks or comments, I could float the Reviewing toolbar and leave it where I wanted to have it, minimizing my need to move the pointer around.
Heh. Touch typing can get out of hand quickly. But you asked...