Reportedly, there is a unique new Twitter application in development called TwittAround. It is an augmented reality Twitter viewer client meant for the iPhone 3GS.
With this application, you can see LIVE tweets from other tweeps around your location i.e. in any place near you. You can even see the amount of distance they are away from you. You can move the iPhone around and watch the miniature display pictures of the tweeps from the location in front.