Ping should get made on iOS, inside the music app.
Just imagine being able to use Ping on iOS, with artists profiles and album discography in coverflow. With custom radio stations, and sharing functions like album sharing instantaneously with your friends. Where you can create your own music library and know what your artists are up to and get live show tickets from the passbook app. It'll be like the revolution of the sony walkman once again, with users immersing themselves in sound gardens that they can share with their friends. It'll be an infinite playlist of songs and iTunes radio stations can make their selves into iOS for the first time or you can make music thats similar to an artist play with the radio genius feature. And for a small fee of 10 dollars for half a year you can have all the music in the world in your pocket and listen to demos from bands that are unreleased songs with soundcloud.com like capabilities. Being able to see amazing iTunes Visualizations when a song plays... and being able to stream the song or playlist to Apple TV's or Macbooks with iTunes running on them, with videos from youtube if there is one available for the song, but use the sound from the highest quality audio version available on your device or iTunes servers. All those songs sitting on old hard drives in Apple Server rooms would have more purpose again.