I would wager you are pinpointed because you are using wireless, and the Google streetView car recorded the name of your access point. They need not have made

I would wager you are pinpointed because you are using wireless, and the Google streetView car recorded the name of your access point. They need not have made streetview of your area online, but it is likely if you are in the US or Canada that they did drive by. There are also other companies collecting this data, so it may not be just Google's. Browser geolocation uses the id and signal strength of wireless access points. But as mentioned in this thread already, that is only one of many signals including your device's gps and rev-ip data.