That answers all of my questions!
It's obvious to me now that I really was overcomplicating the issue!
It would be interesting to see how this could actually be implemented. I think that there should be some sort of middle-ground between automation & user-feedback/intervention, without sacrificing ease of use. Clearly the current user-controlled systems like DC (and even the WinMX trading phenomenon) are somewhat restrictive & frustrating. However, if everything were left up to a central authority, it could somehow be exploited or manipulated and make the network as vulnerable as if it were purely centralised!
Thanks again
TankGirl!