Drodin has ported the classic Linux game, Extreme Tux Racer, to the PlayBook. The game is open source but they are charging $1.99 for it in App World. Either way the classic Linux game is quite fun on the PlayBook even in beta form. This game should give you an idea of what we will see in terms of the Native SDK allowing OpenGL games to easily come to the PlayBook and BBX OS.
You can pick up Extreme Tux Racer in App World for $1.99