The only way I see it could be illegal is in the case mentioned above of someone tresspassing to do so or "cracking" a password to gain access. My laptop connected to someone else's unsecure connection once when mine hiccupped and I didn't realize it until I checked to see why my connection was running so slow. Of course in my case if anyone had complained I do have my own connection in the connect menu, you really couldn't use that excuse if you didn't
Wirelesses can be named anything, seems it would be hard to claim someone knew that a connection wasn't an allowed "hot spot".