Pro Keys == great fun. And even moreso than in "GRYBO" (heh) RB, as you said, there's that element of learning -- feeling that I'm learning how to play a song instead of just hitting the correctly colored keys at the correct time. (I haven't had anywhere near as much time with the Mustang 104-button guitar yet, but it from my little experience there it felt like it'd be much the same way.)

Now I just have to get a keyboard for home instead of getting a few minutes here and there to play at work...