Apple has one of the largest user databases in the world, second only to Facebook. iTunes currently has about 575 million users connected onto the database, and this number is growing at 500,000 per day.
This means Apple could have 600 million within the next two months and could have 1 billion in four years, provided iTunes keeps growing at its current rate.
Having all this user data allows Apple to utilise products with better usage on the iTunes store. We believe the iTunes Radio project will do really well because it is tied into the iTunes experience.
However, we have yet to see a stellar service release from Apple involving a social network. This could be utilised through the huge iTunes database records.