well there are ways to prevent leechers.

1) Require they share some amount of files be it 1 5 10 or whatever amount of Gigs you believe is reasonable. Personally anything more then 5 is not good for the virgin user and so they end up stuck in some smaller hubs or those who are not so uptight about it.

2) Require the user to have a minimum amount of slots available.
This prevents those who only allow 1 slot and download from 10 people at once.

I believe since it is a USER ran network via HUBS and linked HUBS that any problems can be over come.