Recently a man was arrested in Florida, and charged with computer crimes, for leaching a WiFi connection. ZDNet has an FAQ about the case here. He’d driven his Chevy Blazer around a neighborhood, found an open WiFi access point, and was using it.
In my neighborhood, devices in my home can reach as many as 5 different access points in addition to my own. My access points are WEP secured. If necessary I will go to MAC address filtering. Most of my neighbours do the same. However, WiFi access points broadcast in public, unlicensed spectrum. They reach far beyond the boundaries of individual property.
So, if a user of public spectrum is broadcasting an unsecured signal into a public space, then who is liable? My contention is that the intent of the owner of the access point must be to share it.