A buddy of mine used to make money by going to houses that had unsecured wireless networks, explaining the risks, and charging them $25 to turn on encryption. The hardest part is figuring out which house belongs to a particular network. He said he used some little handheld device with a semi-directional antenna and a signal strength indicator, I imagine something like http://www.hawkingtech.com/products/productlist.php?CatID=33&FamID=102&ProdID=198.
I'm considering trying the same thing, but I don't want to buy that device; I'm sure the same thing can be done with my laptop. I bought a super cheap USB WiFi adapter with a place to plug in an external antenna, then I made myself a "cantenna", but when I use it with NetStumbler, pointing the can in different directions doesn't seem to give me significantly different signal strength readings. Possibly because my little USB device is super cheap?
Is there a better way to determine the source of the signal, or am I on the right track and I just need to tweak/invest more?