Is it "Theft" to use someone's unsecured wireless network without their permission? No. It is trespassing. This the same as you sneaking into someone's house through an unlocked door and making free phone calls on their phone.

Is it "theft" if the owner copies any passwords, credit card numbers, and interesting porn that send over _his_ network? Yes it is. It is the same as someone letting another person use their phone and recording any financial information from the phone calls.

Now, I have a heavily secured network at home (encrypted, hardware firewall and software firewalls on all of the computers). I also agree that it is stupid to run an unsecured network and pass private info on an unsecured network.