I had a better idea the other day: comparing app coolness factors. You would meet somebody who also has an iPhone, and an automatic coolness factor of your apps would be calculated (details are a bit fuzzy, maybe it could be calculated from Facebook Likes per app or something like that). Then you get to compare the coolness of your installation base.
I see an urgent need for this since all iPhones look the same. Therefore there is a need for individualization by installing individual apps.