Google will tell your mates where you are
If that's what you really want
Google's Maps for Mobile just went social, with the launch of Latitude; a service that automatically shares your location with selected friends who might want to know where you are.
Enrolling in Latitude is just a matter of downloading the latest Mobile Maps, or the desktop gadget for those the non-road-warrior just wants to keep track of their friends, or enemies. Location is established using GPS, or celltower idents that Google has already accumulated for the MyLocation service, and is shared with those one selects using the Latitude interface.
Google claims not to store any location information, other than the last update, and location sharing doesn't have to be two-way - when a friend offers to share their location with you, you are at liberty to keep your location secret or share only to city-scale, as the "latitude privacy" video shows:
You need to have Mobile Maps running the whole time, obviously, which cuts out iPhone users for the moment, though there's talk of a workaround. Running the application the whole time is going to have a significant impact on battery life, though we can't tell you how much as when we tried to use the service it wasn't allowing us to log on.
If you feel the need to share your location with the world then you're probably already doing that using Twitter or similar, though this could save you some typing. More concerning is when your boss asks you to give the software a go - automated time-and-motion studies for free, and companies selling commercial tracking systems should be concerned.
Google isn't storing historical location information, unlike your cellular operator, but should the service become popular then it won't be easy to ignore the revenue stream such information represents. Potential users might also like to consider what happens when they do decide not to share their location for an hour or two - creating more questions from curious friends or colleagues than might be welcome. ®