Yes, it is.
When you have a device such as a cellphone or a BlackBerry, it has often built into it the ability to help you locate yourself. Most modern devices now can use three technologies simultaneously: GPS, if you can see the GPS satellites; the cellphone tower information from whatever cellphone towers it's able to see; and also this Wi-Fi data. When you walk into a strange street you can determine what satellites are visible, but also whether there's a Wi-Fi from a local coffee shop, or from the Joneses next door, and that information can be used to recognize where you are.