I read this thread a few days back and only remembered the L1 & R1 shortcuts.
In the last couple days I remembered the start button at the home screen, discovered about the L3 to pause the scrolling text, and I also discovered (while doing S16) that you could switch between the DFP display and normal gauges when the game is paused. I thought for sure that nobody else would have noticed that yet. But alas, I am too late on that one. However, I do have one that is not mentioned here so far...
In Photo Travel, while on a selection at the right (no matter what it is) the shoulder buttons provide you with a toggling hot-jump to the 4 main buttons on-screen. L1 takes you to Camera Direction, L2 to Camera Tilt, R1 takes you to Camera Position, and R2 to Camera Height.