I heard about this today on Working lunch, its pretty "old" news.
To start with, how to do it is so easy.
-- Either park up and scan using built in windows
-- Buy $30 gizmo that can scan whilst driving and show how many secure and not secure points are around
TO PROTECT yourself is even easier.
-- First make sure you have WEP/WPA enables
-- You can set up an ip range for the no of pcs in the house, or even better, manually set ips so the router doesnt give em out dynamicly
-- You can set most routers to accept specific mac addresses.
TO FIND OUT if some one is using you internet
-- Most routers list who is connected to it, shows there ip and there computer name, and it keeps a log, you can check the log, if you see a name that doesnt match one of your pcs, then it logs the mac address, this is what you can give to the authorities.
Its pretty serious stuff, as most people leave there system on MSHOME or other default workgroup names. And then a fair few dont even have a password to log into windows. I have done this to my partner as a joke to show her how stupid these two errors are, i logged into to her computer from outside and got her bank details stored in my documents. So many people do it, BBC did something about this too, there are even wifi decoders that can tap into the connection and decode info been sent, this was also featured on the BBC.
I think the best solution is to protect yourself, and like a poster did a few ones up, if you do detect an unsecure connection from your computer in the house, go and tell them how to sort it, or you could find people downloading all sorts of nasty stuff using your connection, inc illegal material, software and in cases commiting fraud and scams or using it to send spam.
Oh, and as for doing it, its so simple to prove if your stupid as windows logs what it connects to and the router logs who connects to it, a clever hacker would have something deleting the log on the laptop and delete the log on the router as most people dont even set up a password for the admin on the router.