Brightkite has released a native iPhone application to interface with their web service. Brightkite is a location-based social network in which you can see where your friends and what they are doing. Features in version 1.0 include:
* Auto geo-location including Place Snapping and Pick a Place.
* Posting photos and notes to places
* Nearby people and activity feed
* Friends list and activity feed
* People, places and posts search
* Threaded messaging
* Profile streams
* Place streams
* Commenting on posts
You need an Brightkite.com account to use the application, but is otherwise free.
App Store Link: Brightkite