Although Apple has caught a lot of heat lately over the location-tracking issue that was recently resolved with the iOS 4.3.3 update, there are several apps out there that do track where you are with amazing detail. They range from Find My iPhone to apps such as Footprints.
Footprints for iPhone and iPad runs in the background with minimal battery drain and tracks your movements in real time. Once you go through a quick setup process and permit someone to see your movements, they can trace wherever you go. There's a parental control feature that prevents kids from disabling the tracker.
Using Google Maps, you can see where the person you're tracking is and how long they've been at that location. Call it Google Latitude for the very paranoid. However, unlike the location-tracking data issue with Apple, you must grant permission to people who want to view your data. The app's developers tout it as not only a way to keep track of kids and spouses, but employees as well.
Footprints is a free download, and the first 60 days of the service are free. After that, you can do a 3-month subscription for USD$0.99, yearly subscription for $2.99 or 2-year subscription for $4.99.