Tim has added a section to his Broadband Security article about Wardriving. Here's a taste:
I actually knew a guy who took this a step farther and wrote a program on his Commodore 64 that could spoof the phone company computers and let him make "free" long distance phone calls...well, at least free to him...but I digress. In the modern day of broadband and high-speed internet, people have migrated from modems to routers, many of which have wireless capability. "War Driving" is the act of driving around in a car looking for "open" wireless access points, usually with a booster antenna on the roof that is attached to a wireless LAN card in a laptop. But these days, this can also be done with a PDA, like an iPAQ. Read more over here.