I'd suggest you hook into a browser API to do this. I believe google maps already do this via a "my location" button, which can estimate, at worst case, to the

I'd suggest you hook into a browser API to do this. I believe google maps already do this via a "my location" button, which can estimate, at worst case, to the city usually. Also, changing the default and saving it per login would be good, ala google maps too.