I have a cool rhythm game called "Sequence", and it dynamically utilizes 3 arrow sets interchangably. Each set has a feature to it.
To be honest, I think I had the second set come into the scene almost accidentally. I was designing the scene and knew I needed more than just one set (since I planned to have the game be landscape or square at thinnest). So I threw in an extra set, decided it could be used for multiplayer (2 players - 1 keyboard), and just went with it. Then I decided that, since I don't expect to be creating any more songs, that I would start the song off easier and make it get more difficult to try to give the best of both worlds.
So that's the story. If the game becomes popular, I may re-code it to make it so that additional songs and difficulty levels can be utilizes. Likewise, I may release an open version (free .capx) so that offers can expand upon it or use the events for their projects.