In the Date and Time System Preference pane there is now an option to enable “Set time zone automatically using current location”. Assuming you have a Mac OS X computer with Wi-Fi and you use this option (which is not enabled by default) then your portable looks up your location automatically using the wireless access points surrounding you, which can then be looked up against the Skyhook database API and then changes your time zone based on your physical location. However, if your system looks back to the IP address of the KDC and sees a time offset that is greater than 5 minutes a few people have asked me whether that could be problematic. The answer is no. Reason being that the time is relative, based on your time zone setting.
Therefore, even if your computers time changes provided that the relative time to the time on the KDC (be it Active Director or Open Directory) is accurate then you should still be in good shape. Overall, this is a great new feature of Snow Leopard. It’s been integrated into Firefox as well (in your about:config page look for geo.enabled) and I’d expect to start seeing it on a number of devices and in a number of applications that can be geography-aware without having to implement GPS.