For several years millions have shared the places they've been using the Where I've Been website and Facebook application. The site also has an API (our Where I've Been API profile), which allows for much of the same functionality, such as searching countries, marking it visited and adding content such as a story or photo.
The API has an impressive array of methods. Many are accessed via OAuth, which means that users provide your application permission to access their data. Twitter, as well as several other popular APIs, also use this method, more secure than sharing passwords.
Developers of mapping mashups might take specific note of the search and place methods. Developers can find cities by latitude and longitude coordinates, which would allow for some interesting mobile applications, such as logging road trips. Additionally, countries and cities can be searched by name.
While the Where I've Been API looks useful for retrieving locations, it's obviously been built to support the site itself. Therefore, the extensive user methods are best used for social travel sharing, the same thing that has made the Where I've Been product so popular.