Once you are in the iPhone Home Settings you will see that the top block is directly dedicated for the functionality of the iPhone Home button. Here you will see a number of different options for what a double click of the iPhone Home button will do. Your base use of the iPhone Home button will stay the same, but now you can customize what a double press can do.
The default setting for this will be Phone Favorites, but you can also set it to bring up the Search prompt, open the Camera, signal the iPod section to open, or have the same function that a single press of the Home button will have. This is going to be a preference option, but having this set to Search is one of the more useful functions that does not give preference to an iPhone feature.