I wouldn't recommend using some strangers wifi. Like instance, I use to live in apartments. I would purposely leave my network unsecured and run ethereal/cain and abel, any other types of network protocol analyzers (sniffers). I never did anything, but it was funny how I made the networks name "haxin your interwebs", or "don't use me", and people around me would still use it. I don't think it is illegal to use an unsecured network. It's cracking a wep network and using it that is illegal.