The ribbon, when controlled with keyboard by pressing Ctrl, doesn't respond to keystrokes when processing the last one. I was using a MacBook2,1 that's perfectly suitable for writing scores with Sibelius 7 but I always have to slow down to use the ribbon with keyboard. It's very annoying since it distracts me from my fast-paced workflow. Keyboard buffer for Ribbon requested!
Update: Just got a new Retina MacBook this year. The ribbon is still unbelievably slow to respond! I'm inputting all the right key sequences but often I have to try again because the ribbon doesn't listen to my keystrokes quickly enough. This slows down things a lot in the long run.