Latitude is Google's location-based service that lets you see the location of your friends on a map and share your own location. This sharing is done in real-time using your phones GPS receiver and mobile broadband connection. The app originally appeared back in 2009 for a moment, but Apple pulled it from the App Store. According to Google's mobile blog, Apple suggested that Latitude would be better served as a web-based application and not a standalone app. Unfortunately, a web-based app does not have access to the core iOS APIs and can't access key background GPS data. Without background GPS information, real-time updating was not possible, and the utility of the web-based app was greatly diminished.
The new version of the Latitude app has been updated to support background processing on devices with iOS 4.0 or greater. Now with access to background GPS data, the Latitude app will continue to share your location in real-time, even when the app is closed or the screen is locked. This background location reporting may be a welcome feature, but don't forget to turn it off when you are done tracking yourself or your friends. You would not want Latitude to inadvertently track you to the movie theater when you are supposed to be at home sick.