I have mine set to the left side button on my mouse. It makes it so much easier to switch firing modes or jump back to my rifle. I saw a huge improvement in my playing after I tweaked all my keyboard settings. I noticed that I could never switch to my knife fast enough to make use of it. I made it the scroll button (mouse button 2 I think) and it just took off from there. In
BF2 I made the parachute button the delete key because it was big and easy to find and I kept missing it when I tried to hit it. I highly recommend to everyone that they take the time to try different settings until they find one that works better for them. Having extra mouse buttons is a huge advantage.