Aaron Swartz has written up a warchalking FAQ that addresses the shibboleths and paranoia about discovering, marking and using wireless connectivity.
Is that illegal?
Although I am not a lawyer, I don't think it's illegal to make chalk marks on the sidewalk. I know a lot of hopscotch players who'd be worried if it was…
Well, is it immoral?
Not at all! Warchalking is a helpful service to assist people in finding something they need (an Internet connection).