The first function that came to mind was the use of two buttons for acceleration and breaking during a racing game. The demo of Colin McRae DiRT was used, as it offers all three types of driving: dirt, asphalt and dirt rally. The game also requires the constant use of well placed braking, which makes it a good test to figure out how accurate one can be with the Fragpedal Elite.
Even though you should be used to such a configuration if you have a drivers licence, I had my difficulties. The buttons worked great and at no point did I have any problems with the buttons not responding or not working. Nevertheless, the "press and hold" feature is not very comfortable with the round buttons. While you will feel these playing bare feet, nothing is felt when on the pedal with shoes or slippers. It would help a lot if pedals were used instead of buttons, or if the Fragpedals could be raised just like a keyboard, to allow for the heel of your foot to stay on the ground. As they are now, you will find yourself raising your heels to excert the needed pressure on the round button.
If you can get used to that, they work great in DiRT. While they do make a nice addition, stick with your steering wheel and the traditional pedals if you play racing games exclusively.
To give another type of game a shot (all the pun intended), I tried the DirectX 9 demo of Lost Planet. I simply used the pedal as left and right mouse button setting for shooting primary and alternative weapons. This worked great. You can also assign the other two to crouch or to to release the hook in the game. It actually works really well once you get used to having additional buttons at your feet. In this case the shape of the buttons was not such a problem, as we do no associate "shooting" with having a pedal at our feet, but we do look for one when accelerating or breaking in a car.
The response of the buttons pressed is very good, but one button has a "click" that you can feel when pressed the other does not. Getting different types of feedback from two identical buttons is not ideal.