In May 2008, I had posted about how great it would be if Google Maps (Mobile) would add the capability for users to 'Sign In' to the service since that would automatically add the capability to track one's mobile phone, if lost; without even needing to have a GPS capable handset.
Well, finally - its here! As an update to existing Google Maps Mobile, it is not primarily intended to help you when you're 'lost' but to share your location with your family and friends, in real time!
Its called Google Latitude. Check it out! As usual, here's the YouTube video intro: