Google Latitude is a new feature of Google Maps on your smart phone or other mobile device which lets you see where your friends are at any given moment. — Friends who have opted-in to Latitude and want you to know where they are, that is.

As the Official Google Blog explains:

Once you’ve opted in to Latitude, you can see the approximate location of your friends and loved ones who have decided to share their location with you. So now you can do things like see if your spouse is stuck in traffic on the way home from work, notice that a buddy is in town for the weekend, or take comfort in knowing that a loved one’s flight landed safely, despite bad weather.

Sounds great… But what about privacy?

Everything about Latitude is opt-in. You not only control exactly who gets to see your location but you also decide the location that they see. For instance, let’s say you are in Rome. Instead of having your approximate location detected and shared automatically, you can manually set your location for elsewhere — perhaps indicating a visit to Niagara Falls. Since you may not want to share the same information with everyone, Latitude lets you change the settings on a friend-by-friend basis. So, for each person, you can choose to share your best available location or your city-level location. Or you can hide. Everything is under your control and, of course, you can sign out of Latitude at any time.

Latitude also works on your desktop or notebook computer, using the Latitude iGoogle gadget.

Latitude is already available in 27 countries worldwide and Google is working on adding more.

Visit the Latitude Web site to see if your smart phone is compatible with Latitude. You’ll also find links to further details and installation instructions.