I have a touch screen and a SpaceNavigator (using RBC9 driver). I find I use the touch screen only when I'm setting a nav location or adding songs to a play list. I use the SN for volume (rotate left right), play/pause (short press down), media/music menu (pull up), main menu (long press down), next/previous track (slide left/right), menu/list scroll up down (slide forward/back).

The device also has rock left/right and rock forward/back but I don't use those. I had originally had it set to rock left/right to fast forward/rewind the song but never used it so I disabled it. One of the benefits of this device is that you only need to grab one knob and not worry about finding any other buttons for control.