crossing the property line just adds trespass if you do so. it's the use of / taking something that you have no legal rights to.
also the possible side effects of the use.
say joe has wifi and leave it open, say bob uses it and some other person.
later the police/fbi or other law enforcement find that joe's wifi was used in the commission of an electronic crime....
now bob may be taken to court / arrested etc.... as he might be the one who committed the crime.
a hassle and very embarrassing to say the least! even if you prove that you did not do the major crime you could still be found guilty of the taking of services!
SO is it worth it to run the risk ?? not to me, I will pay for my own thank you!