I have been playing with a wifi sniffer for the last little while (the
Nx) and re-discovered an interesting information leak. This is widely known, but it wasn't known to me
If you have associated your iOS device (or Mac) with a wifi access point, every so often it broadcasts a list of all of your associated access points. With any of the freely available AP location tools, it is trivial to get a good idea where you work, live, and like to hang out.
Furthermore, it is a simple matter of scripting to set the SSID, and If it's a well known SSID (for instance, a hotel or restaurant) I can set the passphrase to be the same and you'll just snap on to my network.
I tried Windows, Windows Phone, and a bunch of Android devices and they don't have this same behavior.
Be careful out there.