But yeah, making a facebook/twitter-style social network app that uses plain email as transport would be really cool.

Probably. On the server-side RSS is nicer in some respects - you're not sending out mail to old, disused inboxes, you don't have to manage subscriptions or worry about being blocked as spam etc.

One thing that I think might make email better is if people got used to the idea of "email apps". The idea that my inbox might collate stories from a given source into a scannable digest (like RSS might give me) seems like a strange departure from the traditional idea of what an email client or service is "meant to do" - present discrete, unmodified messages in the most transparent way possible.

For a social network it's clear that you'd need something like that, though - you'd need clever filters on your feed, thumbnails on images, possible integration with image-sharing services etc etc. Using email and mailing lists gives you a big head-start, but if you can't build on top of it then it can't take off like a dedicated protocol can.

I can't help feeling that the natural outcome of decentralized social networking is that people eventually start hosting them for mom and dad, then a few friends, then start companies, then we are back to facebook. Someone, somewhere is going to have to have a database of names mapped to servers.

Centralization is, in an abstract way, present in so many of our social structures, that yes, I disagree that within a capitalist economic structure (one which is optimized for sharing of services rather than individualism, ie: non-technical users simply wont do this unless the work is done for them, like facebook did) it would be next to impossible for something like this to work.

People quite simply don't want to deal with this shit, and centralization brings efficiency and management amongst many other things.

But nothing stops most of us in the free world from choosing an alternative root system. Other than the support cost of a minor config change in our OS or application software.

The difference between DNS and Facebook/Twitter is that DNS is regulated so that bad guys have to go through some kind of due process to shut down your domain. It's not perfect, but it's better than what else we've got.

DNS is really only optional for email, at least functionally. But I think a lot of people assume there can be no email without domain names.

Instead of another service that will essentially turn into DNS, I would propose just using DNS for naming. So if you're Tyler Durden you register tyler.durden.name and put an A record pointing to your DiSo server. Now you can switch providers while retaining your identity by just changing the A record.

    The original BitTorrent client was the first to offer decentralized [...]

Facebook is the opposite of this. I have no option to build my own site for facebook style networking. I have no option to subscribe to Google's implementation of a general social networking protocol.