Hi - I am a newbie as well and while I cannot give you an answer, I am also interested in knowing this. For my project I want to flick a switch or press a button and when the button is pressed I get a text message to my Android (Galaxy Note 2 for now). I found this e-book at my library: Beginning Android ADK with Arduino, Mario Bohmer. It has quite a few projects and while I have only read the first couple chapters may help you in the future - just thought I would suggest, if you had not come across this.
Also, I have an Uno already and for the sake of saving money wanted to continue to use it for my project and implement the USB Shield. The book mentions that the libraries have been configured for the 2560 but can implement the USB Host Shield to an Uno and originally the code was designed around the Uno. I found that the code is hosted on Github: USB_Host_Shield_2.0/README.md at master · felis/USB_Host_Shield_2.0 · GitHub
GitHub - felis/USB_Host_Shield_2.0: Revision 2.0 of USB Host Library for Arduino.
I believe this may help answer our question on what code to change or keep the same depending if you are going to use the 2560 or the Uno with the USB shield. I am not the strongest programmer but have some of the same experience you shared and wondering if there is a copy of the original code utilizing the USB Shield and the Uno. If you come across this Please be sure to share! Thanks!!