Does MAC filtering at the router level help at all? If the backup option is turned on, does Google also save your MAC addresses? If not, that seems like a good start to prevent someone from connecting to your network, even if they know the password. Obviously this won't help for public hot spots, but I always assume that public hot spots are already open to anyone. What if you are connecting to a Wi-Fi network using MSCHAP or MSCHAPv2? Does Google now know my domain login and password? That seems like a huge gaff.