The buttons on my controller had became a bit lax of late, taking more and more pressure to register. I opened up the controller, cleaned the black part of the rubber moulding and the circuit board and then took a piece of double sided sticky tape, removed the layer on one side and stuck it to a sheet of foil, turned it around and placed a little piece over the original black contact parts on the rubber.
Heat it up with a hairdryer or similar to ensure it gets a really good stick and put the controller back together and voila, back to its original razor sharp goodness. Here's a pic (not of mine) to give you a visual:
