It may be worthwhile to compare the success of ping in increasing sales to the success of Genius in increasing sales.

I don't have bulk data on this at all, but I can say that personally, I've bought songs and apps that I've seen recommended to me on their respective Genius lists, but I've never bought a song that a friend has recommended.

Is the genius algorithm more meaningful for sales than social connections? In my experience, yes, algorithm beats friends.