Hey I agree, sitting in somebody's business, just to suck up their WiFi is not very cool.
If I am away from home, sure I use free WiFi all the time, but I try to be not as rude and sit in the parking lot in my car, and use it.
A lot of places do not really care one way or the other, I know I have asked many business owners about it.
Take my local McDonalds for example, they actually like people to sit there all day, but plastic seats are not very comfortable so few do it.
They don't care if you buy anything either.
Me however, I am a tinker/hobby engineer, and found a solution, that McDonalds is a little bit under a mile from my home, and with some info I found online, I built an antenna that let's me pickup WiFi several miles away.
So hey if its free go for it.
Wanna build your own ? Go here
How-To: Build a WiFi biquad dish antenna
Mike