Tonchidot's Sekai Camera is the killer iPhone application I was looking for: just point your camera anywhere around you to have instant feedback about whatever is on your screen. Directions, reviews, messages, offers, and any tag you can imagine will appear floating in front of you, adding a graphic overlay to the world.
Tonchidot defines their amazing Sekai Camera—in Japanese, World Camera-- as a "social tagging device" for the iPhone. It combines most technologies in the iPhone 3G, from the camera and the GPS to the internet connectivity and its microphone. When you start it, the application first checks where you are using the built-in GPS in the iPhone 3G.
At that point you can do two things. One, you can see information about places and objects around you, overlaid on the real-time video. Two, you can add your own information, whether you are an individual, a business, or any other kind of organisation. You just point and add your tag, which can include text, images, and sound. [Tonchidot via Dvice]