I have been hearing a lot about FON recently.
Basically you have a router which creates two wireless networks, one for you and one for other FON users.
Then when you are out and about you can access the net through other FON networks.
Personally I think it’s of little use, as how often are you in a residential area and need net access. Generally I need net access when I am in the centre of cities or in transport nodes.
So if you want to share your internet, FON is a good idea, less so if you are going to depend on it for net access.