Brightkite is a relatively new service, still in private beta, that combines Twitter-like microblogging with location-awareness. Up to this point, it's taken that location via user input: you type your address into Brightkite or alternately have it search for the location based on a business name. This is a clunky way to indicate location, which is why I rarely use it. Obviously, getting coordinates directly from a GPS-enabled phone would make the service much more useful.
Unfortunately, Brightkite's iPhone 3G app does not take GPS input. This is a big issue, and I am not sure how Brightkite will recover unless it can pair a GPS-enabled client with another major launch such as the upcoming Android or RIM touchscreen launches.