Gamekey? (Plug 'N Play)

OKay, so I was at Wal-Mart about a week ago, and I saw the new Plug 'N Play controller (this time it's General Grievous instead of Darth Vader). It has the same games so I didn't give it much thought untill I saw the back, where there was an advertisment for a "Gamekey". A Gamekey is a small cartidge that fits into the Plug 'N Play controller and holds new games, like a booster pack. Does anyone have any other info on it, like what kind of games the Gamekey will have, when it will be released, if it will work with my old (Vader) controller, ect?