Correct me if I'm wrong, but I think it was the Gamecube controller (again ! sry...) that introduced the pressure sensitive shoulder buttons. But it was barely used, I think FZero GX and Wave Race Blue Storm used it.
Imho it's a very nice feature in racing games because if feels like an advancing gameplay tweaking, and I kinda like that. However, I hated its use in Heavy Rain. Maybe an underrated gameplay features...







