@wander - I think a lot of people probably use their built in WiFi sniffers to find any network that is available. I know for myself my MP3 player connects with whatever network it happens to come across in an area automatically. As long as the network isn't password protected my MP3 player will latch onto the signal so I can enjoy surfing the web at no cost.
I think that if people really want to protect their bandwidth they need to put a password on their network. For myself I think nothing of downloading a movie or several songs on whatever network I am attached to. I am sure that adds up for someone, though who really knows. All Internet providers have different bandwidth limits.