You'd get drafted into storing images for some subset of the intersection of your social graph and several others, and the rest of your images would be served by someone(s) with whom your social graph intersects.
Presumably invitations would be via e-mail, or, if you wanted to be even more decentralized, QR code.
As far as data volume, I've got to imagine the data usage per user would be significantly less than BitTorrent.
The desirable aspect of this system is obvious - the only people who see your data are people who've seen a QR code from someone in your social graph - your FaceTorrent profile will never, ever be indexed by Google.
What if Google started offering, say, free Google Coupons (assuming they roll their own groupon) in exchange for befriending them on FaceTorrent? Not all of my friends and relatives value privacy as much as I do.