Easy to say how Gnutella Dev. can push the people to share!!!!

Build the client so when other's clients connect, if the connecting people don't share enought or don't give enought BW to the net they are stuck to low level performance.

Don't Share?
I give you only 1/2 kB/s of content (so you pay in time what you save don't sharing) and always serve you after the sharing people (maybe also I say you why)

If one have not big share, demote it on the queue.
Maybe divide GB/time waiting, so more you share less you wait.

Bottom line.
DC is more elitist because it allow few leecheers, but it work.