it's called warcaching, you drive around looking for open wifi from peoples homes.
well on the way home from work(surrey) I found 171 wireless accesspoints.
60 of which were secured.
which means I have a high probablity of using 111 other peoples internet.
without them knowing.
I found a software called netstumbler which constantly checks for wireless networks and
lists them and also asociates them with an attached GPS, so it will log the found wifi and where you found it.