Wirelessly posted (Mozilla/5.0 (iPhone; U; CPU like Mac OS X; en) AppleWebKit/420.1 (KHTML, like Gecko) Version/3.0 Mobile/4A93 Safari/419.3)
I don't think they drive around mapping the mac addresses. I just moved to a new house not long ago and it uses my wifi and puts a little circle around my house. Unless they drove by a few days ago.
Not to mention I'm a student in the little college town of Springfield, MO. Doubt they would have my town mapped.
Some observations: When it uses wifi to locate, the circle is much smaller and zeroed in. Cell triangulation can vary from a circle 5 blocks wide to 5 miles in my town, though its usually less then a mile, and there are cell towers all around. Walking to campus, I kept refreshing it and wifi tracked me in half block increments most the time over a mile. This is a college student neighborhood where people move all the time and the mac addresses would also change. I think its also ip based.