Having an iPhone with GPS and location-aware applications is incredibly useful when exploring a new city. For example:
- Just arrived? Fire up Locly and see all the nearby places that are mentioned in Wikipedia, with distances.
- Feeling hungry? Open TripAdvisor (or UrbanSpoon if you're in a major city, or there are probably other apps for other restaurant/café review sites as well) and see ratings and distances for places to eat nearby.
- Want to see a film? Showtimes has locations, distances and screening times for all the nearby cinemas.
All these apps have links to Google Maps, and when that opens you can instantly plot a route from your current location.
The main thing missing is a 'plot all these on a map' application, or even directions, so you can see which things are close together/in a certain area.
Twinkle has tweets from people nearby, but there aren't many people using it at the moment; when they are it will definitely need some filtering.