With more and more smartphones now including Wi-Fi, initiatives such as FON are very welcome indeed. See the E-series blog for an intro to the subject of free Wi-Fi wherever you are in the world and on how to get started.
This is a great idea, but I think it'll run into the same legal problems as unsecured wifi routers.
If you say that people aren't responsible for whatever's downloaded through their modem, then anyone could download as much illegal material as they want.
If you say that people ARE responsible for whatever's downloaded through their modem, then unsecured routers and things like Fon will potentially land their innocent owners in legal hot water.
Police internet sting operations tend to work by tracing the IP address of the person accessing illegal files, and if you have a Fon box the IP address could end up being traced to your house because a criminal used your Fon connection. What do you do then?
It seems that this topic is already preoccupying Fon users: