Thank you for the snippet. 
Concerning the games/platforms I've managed to interface the Esplora with, I didn't change anything from the EsploraKart example, but I can list what I managed to get to work-
On Ubuntu
SuperTuxKart, SuperTux, various PyGame+Processing builds including versions of Frogger, Pacman and Space Invaders, a couple Flight Simulator Games from the Ubuntu Software Center, Even some Linux games available from Steam worked with the Esplora (though the button mappings fell short which is why I asked about the Slider)
On Raspberry Pi-
SuperTux works perfectly! However, I couldn't get STK to load properly, even though its available in the Repo. There aren't too many games available via the PiStore as of yet, but that will change with time.
On Nexus 7-
SuperTux again! But like the RPi there was no STK for the Nexus that I could find... Thus far Android Gamepad support is somewhat tricky but by no means impossible. Several games (like Grand Theft Auto and Modern Combat) advertise native USB gamepad support through the Jelly Bean API but thus far I have had no luck. Seem entirely workable though.
I'm still working on mapping out that SPI header to my Seeed Studio XBee Shield so as to try out your fantastic XBee hacks BTW. Serial Communication is still something I'm slowly digesting, so it might take a little longer...
Keep up YOUR great work!
P.S- You may have noticed a similar post I added to the Adafruit forums-USB Gamepad 3.0 - adafruit industries Though so far it hasn't gotten any bites...