I built this tool Super Snooper which is a box that sits on my dash and logs wifi points as I drive around. Looks a bit steampunk but it works.
I can specifiy open or closed points if I need. It will log the access point name, MAC Address, Signal strength, logitude and latitude as well as security type to a SD card on the fly.
My original idea was for Skyhook but they use PDA's with wifi and with mobiles coming out with GPS in them I think wifi postioning is dead.
Perhaps I will do a segment on how to make one lol.
For the hardware freaks.....
GPS - EM-406A
SD card controller - Microdrive
Controller - Picaxe 28x1 (program in BASIC)
WIFI - Lantronix WiPort