The first being, that's stealing. And I don't support it.
The other, is that it is a federal crime to connect to networks that are not yours and have no authorization to do so. Check out the 1984 Computer Crimes act, and 2001 Electronic Crimes Act and Title 18 U.S.C. 1030 of the US Federal Crime Statute.
Your best bet:
Get an Internet connection of your own.
It costs 20-30 bux a month, and well worth it.