I like the Pandora keyboard layout, it works well for me. I'm not using the shift-button (left shoulder is much more practical), ALT is not very convenient, Tab would be nicer as a separate button, and I don't know how to get the DEL button to work. Other than that, everything is perfect.
So perhaps the shift-button should become Tab, and L2 and R2 buttons (assuming we'll have those) could be used for ALT and Fn (which would free up room for one more key). And only show the labels "START" and "SELECT" on those two buttons (in a slightly bigger font), they can be mapped to whatever is useful (e.g. if someone wants to remap one or two of the shoulder to mouse clicks, START and/or SELECT can replace them).