There's also something else worthwhile remembering.
Most people when they get their wireless network set up at home, they lock it all up and feel secure in the knowledge that nobody is leaching their network.
But when they're given their internet package from their provider, they're given a password, which they are told to change, but most people that aren't internet savvy don't!.
These are usually something like "admin1234" or "user1234" or "password1234" the digits might be slightly different like "0000" and so on...
All it takes is somebody who's a bit more internet savvy and with a bit of time on their hands, and they're in.
I've often over heard people brag about leaching off somebody that lives close by!
So it's highly recommended that you change the password.
And if you're double paranoid, you can always ask a friend to bring their laptop over, and see if they can connect to your network...