Gamer culture: I can't ambi-shoulder-button

I have a confession to make: I'm not an ambi-shoulder-button user. That is, my left shoulder-button skills are lacking. Sure I can get by, and fortunately, most game developers usually don't rely on the "L" button for primary action tasks, but I've never been any good at using shoulder buttons with my left hand.

Any other right-handers plagued with a lack of ambi-shoulder-button skills? What buttons do you find most difficult to use, if any, regardless of your dexterity?