Does Latitude run in the background, or do users need to launch the app or otherwise "check in" to record their location? From what I can tell you have to hit

Does Latitude run in the background, or do users need to launch the app or otherwise "check in" to record their location? From what I can tell you have to hit the Latitude website on an iPhone for it to capture your location (which severely limits its usefulness), but I was curious about other phones.