Way back in 2001 I purchased a Shuttle Pro for use with FCP and ProTools and I have loved this thing ever since (and it still works!) I wanted to share my settings for FCPX that I find most useful. Rather than edit, I really use the Shuttle Pro as a precision frame finding device, and then trimming or marking in and out with that frame. I do a lot of voice overs so I have a dedicated button just for that (use to start and stop recordings). To that end here are my settings for the 3.0 drivers, accompanying usage diagram, and even keycap labels to make it look uber cool.
Shuttle Pro Keycaps FCPX 4 (T. Payton)