GMS,
What you are doing is actually against the law - people have been prosecuted for "borrowing" someone else's wifi network.
There was a thread on this very topic recently - I'm sure that a search will locate it.
LH2,
On another subject, since you benefit from someone else's open wifi, I hope you will be polite enough to leave your own wireless network, if you have one, open for the occasional user to take advantage of. It comes at no cost to you and there is a collective benefit in doing that, as you can see.
I admire your altruism, but unless you can find a way to communicate to those that stumble across your "open" network that they have your full permission to use it, then I suggest you refrain from inciting others to perhaps commit an offence.
SD