Google Latitude added two new applications that make location tracking more useful: history and alerts.
Google Latitude History stores your locations and lets you visualize them on a map. You can remove some of the locations and export the history to a KML file. At the moment, you are the only one who can access your location history.
A more interesting application is Google Latitude Alerts, that "lets you receive and send alert notifications if Google Latitude friends are nearby when you're somewhere interesting or unusual. Alerts use Location History to send notifications only when they're most likely to be interesting to you and your nearby friends."
Google Latitude Alerts tries to be smart by only sending notifications when you're at an unusual location or when you're at a familiar place at an unusual time.
For some reason, enabling Google Latitude Alerts has an unexpected side-effect: "your nearby Latitude friends each receive an alert notification email that you are nearby, even if they haven't yet enabled Location Alerts. Alerts notify friends where you usually are on that day and time to explain why your location is unusual and the alert was sent."
Both applications are opt-in, so you need to explicitly enable them. Unfortunately, even if you don't enable alerts, you may still receive notifications from your friends. To disable the notifications, visit this page and click on "Opt out of notifications from friends".
{ via Google Mobile blog }