Om Malik has a great post about the future of Peer to Peer software. Most of this new software is based on the IM (instant message) metaphor. You have to establish an IM connection with someone and then send them your files. I would rather see a situation where I could simply decide which files (photos, music, ect) I am sharing and those people can come into my machine at any time and grab the files. If I need to get you a document, I just make it available to you and you come and get it. No email, no IM, no nothing. Apple has done something very close to this with photocasting, but it only works for Macs and only with .mac accounts.
Of the products Om talks about, Box Cloud looks to be the closest to what I am looking for. You only need to run their desktop application to share and people getting your files only need a web browser. The catch is you get 1GB of transfer per month. Sounds cool. I will test it out and report back.