Sophos the security company went warbiking in central London and found very high numbers of wireless networks, with parts still without any security or with bad wireless security. All explained with a nice youtube video which presents the results in a format even your neighbour who still relies on WEP can understand. The Sophos warbiking project. Found via Warbiking: WiFi hacken op de fiets - security.nl although I would avoid using the term 'hacking' for purely passive measurements.