Anyone tried this? Its great fun =) [and completely legal]
Basically it invoves driving[or walking] around looking for wireless networks.
all you need is a laptop and a WiFi Card, and off you go. Then you just need some software to scan for the networks and your set to go. Most network cards have built in software to scan - my netgear card does - but there is 3rd party software outthere although the compatability isnt great.
I found hundreds of networks in my town [sale, near manchester], and the scary thing is that 90% of them werent protected! If i were some nefarious cracker [or a nice hacker who wants to help] it would be too easy to log on to the network and do what you want with it....still its fun looking =)