Google launched a new feature in Google Maps for mobile and iGoogle that lets the user share location data with your friends and family online. 
Instead of GPS, the service uses wireless location beacons in the Google Maps database to determine an approximate location. Google users can opt into the feature, and then invite friends and family to join Google Latitude. Once they accept, you will see their profile picture appear on a map through a mobile device or desktop PC.
- Google Latitude is available in 27 countries, and across a variety of devices, including:
- Android-powered devices, such as the T-Mobile G1
- most color BlackBerry devices
- most Windows Mobile 5.0+ devices
- most Symbian S60 devices (Nokia smartphones)
- Google.com users of iGoogle
http://google.com/latitude