Here's another cool use for your GPSr. War Driving is basically using a WiFi equipped laptop (or PDA) with GPSr attached to locate and map WiFi signals ("Hot Spots").
War Chalking is an off-shoot, where folks chalk symbols on the sidewalks near "hot spots" to show others that free wireless is available.
One quick drive through most any town with a WiFi equipped device will quickly prove to you that you should have WEP (Wired Equivalent Protection--a wireless encryption scheme or MAC address filtering) enabled if you have a wireless router in your home or business.
Here's a link to download "NetStumbler"--THE WiFi finder of choice (for most wireless cards).