I'm sure the internet companies try and limit people doing this. Here's the thing, keeping your wireless connection open, there is nothing illegal about this nor could there be. I think in the future, internet companies will wise up and force a private connection on you that is mac address related. Actually selling the service will require a license so it is illegal, however, giving it away for free is not a crime. Basically if you're charging people, keep no paper trail and you'll be straight.
Chief of police gets free internet off my house lol, my dad put up a huge antenna on the roof.
If in a duplex or apartment setting, it would be legal to share one bill if an arrangement could be made.