If you'd like more info on this inevitable purchase, Gamespot posted, in addition to some new screens and brief footage, some details on the game's new "Party Play" mode. This feature is designed to allow total flexibility in social situations. Party Play allows you to start the game with no players, using a playlist of Guitar Hero music as a sort of jukebox. When people decide they want to play a song, they can pick up an instrument, push a button, and begin playing immediately.
This is also where the game's instrument flexibility comes in. Party Play is designed to allow any combination of instruments, in case you want to play Barbershop Quartet Hero.