Latitude is Google’s response to Foursquare, Gowalla, and Facebook Places: A social location check-in app. As far as I can tell, very few people use it. This is ironic since it is probably descended from the first geo-location social network service I’m aware of: DodgeBall. Google bought DodgeBall and then let it disappear.
Google updated Latitude for iPhone to provide a location check-in feature (v2.1).
Unlike Facebook Places and other geo-location services, Google Latitude by default provides your location regardless of whether or not you identify your current (check-in) location. This is probably why few people use it and then only share location information with select individuals (actualy friends and family). There are settings to determine how geo-location information is shared. But, I suspect this is too much busy work for most people to bother with. My view? Latitude is an interesting app that works well with Google Locations to let you know about your movements. However, it is not a great social tool. It joins Google Buzz, Google Wave and other recent Google social networking product attempts as a third tier service.
Google Latitude 2.1 (iTunes App Store)