I think a WiFi sharing social network would be awesome and if it was integrated with Facebook it would be even better. Obviously you can't trust your WiFi to everyone but it's something you already do with friends and family so why not make it as smooth as possible.

I imagine it would be something like this:

The server will not store the key for long, some minutes max and transmission of any data will be encrypted. The owner of the WiFi hot spot will have to approve every request to share his key (individually or all at once). Then the key of the WiFi hot spot will be sent to those that requested it, after that it will be deleted from the server, it won't even get out of the RAM. The people that request the key will be able to do so with just the push of a button (in the ideal case). All this exchange of data, might happen through 3G so it will be as compact as possible (no adds if on 3G, etc).

If in the same physical space this all will be done locally without sending anything to the server. A smartphone app (at most a few megabytes) will be at the center of this. There will also be a desktop client, that allows you to connect less easily but still better than typing. Connect your smartphone to the computer push a button (depending on setting even without this) and connect to the desired WiFi hot spot.

I am one of those persons that feels that everything is invented, but this is something that I feel is lacking.