Try compiling this form with a wifi MAC Address and press Enter (iframe):

The source code is:

#!/usr/bin/python
# Copyright (C) 2010 Kees Cook 
# License: GPLv3
# Find location of a MAC address via Google Location Services
# http://code.google.com/p/gears/wiki/GeolocationAPI
import cgi
import sys, urllib2
import simplejson
import pprint

form = cgi.FieldStorage()
if not form:
    print "Content-type: text/html"
    print ""
    print ""
    print "Enter MAC address to locate:



"
    print 'source'
    print ""
    sys.exit(0)

#try:
if True:
    loc_req = { 'version': '1.1.0',
                'request_address': True,
                'address_language': 'en',
                'wifi_towers': [] }
    bssid = form['mac'].value
    loc_req['wifi_towers'] += [{ 'mac_address': bssid.replace(':','-'),
                                 'signal_strength': 1 } ]

    data = simplejson.JSONEncoder().encode(loc_req)

    output = urllib2.urlopen('https://www.google.com/loc/json', data).read()
    output = simplejson.loads(output)

    print "Content-type: text/plain"
    print ""
    pprint.pprint(output)
    if output['location']['accuracy'] >= 22000:
        print "# N.B. Accuracy of 22000 or higher seems to indicate unknown location..."
else:
    print "Content-type: text/html"
    print ""
    print ""
    print "Sorry, something went wrong"
    print ""

Think at the possibility for somebody to bruteforce Google DB and retrieve these infos.

Starting from http://standards.ieee.org/regauth/oui/oui.txt, for example, i can try 16^6 mac addresses starting from 00-18-84 to get info about FON hotspots and achieve locations in a day or less.

I think this is not illegal as this is what my GPhone actually does. PS: I have not checked against any bruteforce prevention.

Thanks to Kees Cook.