PSP GPS accessory for the most accurate results, but PSPs only equipped with wi-fi access will still be able to use the service. PlaceEngine can determine your location via wi-fi, or you can manually input a train station to see what's nearby.
While most cell phones are equipped with similar services, x-Radar adds a few game-like attributes to make it distinctly PlayStation. For example, users will be able collect spots throughout the country and build a collection to share with friends. Like foursquare, the service will reward you as you discover new places, and you'll even be able to level up an avatar. It's certainly worth a look, provided you live in the land of the rising sun.