Someone finally built what I've thought Wifi always should have been:
http://fon.com/The website appears to be built by Spanish-speakers and it's not very clear, so I'll explain it here, in English.
You create an account on their site. You buy one of their routers or, if you're lucky, install their software for free on your existing router. From then on, anytime another Fon member passes by your place, they're allowed to use your Router's spare bandwidth (so if you're not home - all of it). In exchange for letting them do this, you can do the same - if you travel, and you're near a Fon member's wifi, you can use it, free of charge.
The Fon software solves some important problems. Most importantly, if you want to share your Wifi without Fon you have 2 crappy choices:
A) You go with no password, anyone can use it. This opens you to idiots, who will eventually find you.
Idiot 1: They find your Wifi and begin downloading everything they can over it, slowing anything you do to a crawl, leading you to setup a password and stop sharing even with non-idiots.
Idiot 2: Thinks they're a genius and smarter than you if they find an unprotected wifi, and infects you with a virus to "prove" it. Now you're screwed for trying to share.
B) You password it up and, at best, share it with people who come over. Not much sharing going on.
Fon fixes this. To solve Idiot 1, it makes your traffic a higher priority than other Fon users on your home connection. And to solve Idiot 2, it creates 2 networks: Yours and Shared. Yours is completely separate, so you can go so far as sharing a folder in Windows and leaving it open to writes by Everyone, and random passers-by still can't get at it - Fon users included. So the "genius" going around attacking people for having an open Wifi never gets a chance to talk to your computer in the first place.
I happen to be a lucky owner of a router that can upgrade to Fon for free - I have a Linksys WRT54G - and I'm excited to switch to Fon when I get home.
One cool bonus is they offer Skype software on their downloads page:
http://www.fon.com/en/downloadIf you have that installed on your phone and find a Fon Wifi in another country - you can make international calls right there, for free. What a convenience. You'd probably want to bring the Fon wifi map for the area with you though.