Yeah I love that idea. Plus search. Imagine building your own Google, based on a specialist expert archive of the stuff you're really good at and sharing that out to whoever wants it...and federating it into a giant search engine.
Like Yahoo
Like Yahoo
SearX also came to my mind but isn't exactly p2p.
I think the trade-off here is the latency and data-loss? Or data-loss could be resolved by introducing some sort of redudancy. Like how seeding works in torrents.