GMail has introduced geolocation as a security measure to alert legitimate users that their accounts may have been hijacked.
GMail will try and resolve IP addresses that are used to login to an account to a geographical area and keep track of them. If suddenly the user logs in from a different geographical area, GMail will try and warn the user with a red banner. The user can then check the details of the login attempts and either verify them as accurate—say, in the event of travel—or to acknowledge them as a legitimate hack. In the event of a hack, GMail will offer a link to change your password on the spot.
The alert is not meant to be a replacement for standard security practices, but it can alert users to unauthorized access to their accounts. The service has been rolled out to individual Gmail users, but should be rolled out to Google Apps customers in the near future.