Google's Social Graph API

Google's Social Graph API was released earlier this year.

The motivation:

With so many websites to join, users must decide where to invest significant time in adding their same connections over and over. For developers, this means it is difficult to build successful web applications that hinge upon a critical mass of users for content and interaction. With the Social Graph API, developers can now utilize public connections their users have already created in other web services. It makes information about public connections between people easily available and useful.

Apart from the obvious application to scientific databases (for example, utilising connections such as co-authorship), imagine the same idea applied to data.