That is a separate question. Personally, I think the answer is to make the service much less promiscuous - reduce the number of posts that an individual can share, make the likelihood of seeing a shared post exponentially decline with the distance from the original poster, make the likelihood of contacts seeing a shared post exponentially decline with the number of posts the sharer has previously shared, etc.
In other words, make the service much more like neighbour/friends conversations and less like a broadcast medium.
Biting the hand that feeds IT
