Like desireco42, this instantly reminded me of BBSes and the days of FidoNET. While running point-to-point wireless would certainly be fun, there are infrastructure limitations (namely, roof access) that may make this project hard to achieve.
I'd much rather see a revival of a network of BBSes using POTS lines. FidoNET went to hell decades ago but the protocols and software are still worthy. It would be fun to use Fido tools (mailers, tossers, editors) to create a fun, off-the-Internet electronic forum.
This probably sounds crazy to most of the younger crowd, I'm sure. I just wish that those who grew up without modems could experience the joy of hearing your phone line ring and watching your BBS answer and receive some mail from someone on the other side of the world. The messages were routed from peer to peer by folks who were willing to pick up the tab to make long distance (and international!) phone calls.
Verizon and AT&T are currently working to change legislation so they can remove POTS completely. Don't expect it to be around for more than a decade except in some high-density urban areas for banking perhaps.
I'm totally from this era but I don't quite have the nostalgia for it that you do. I definitely remember the joy of getting mail when the idea of spam was nonexistent, but I'm not sure I'd want to go back. That said, the protocols people want to run on top of this would be whatever people want, I would think, so if you can find enough people who wanted to do this I don't see what's stopping you. :)
Any chance the administration of nodes for this kind of technology could be crowdsourced to the people in the neighborhood as well, giving not only access but useful knowledge and a learning experience? I know when I was young I didn't need new or expensive technology to hack on - just needed something I had regular access to.
I should also say that the requirements aren't an all-or-nothing deal. For every node we setup we'll need people to use the network, support it, talk about it, and help maintain it. So really, no one here should be discouraged if you don't happen to have access to a semi-tall building. Please - join up and be part of the group - don't let the building access issue stop you.
I suppose this also doesn't require roof access in many cases. If someone is willing (and your building super isn't going to get angry at you), you could put an antenna on a balcony the same way people would put up a satellite dish, and we get could get line-of-sight going at least in one direction from a given building.
check out thefnf.org, they are currently trying to organize the different mesh networks.
In Spain we have the guifi project www.guifi.net/en which works in infrastructure mode, but we are migrating to a new system called qmp and which is mesh based. This firmware is 100% auto config, and works natively over IPv6. The project came from the www.battlemesh.org hacking sessions, where they created the batman protocol.
If anyone is looking at building a mesh network, check tout these systems. They make it so much easier (and cheaper) then it used to be.