From Social Patterns
Social Networks rely on the content provided by the community in general. And in doing this, the members of the community share a lot of data with the website.
For instance, a user might maintain a list of her friends on the social network. Over time, this network grows, and so does the user's interactions with the members of this social network. As the user continues to interact and manage her social interactions on this platform, store photographs, videos, documents, and other content, the power of the platform passes from the user (the very premise of Web 2.0) to the social platform. Switching to another network gets increasingly difficult since the data is on a particular social network without any way of backing up, storing, or importing this data into another system.
Data Portability addresses these concerns by providing an open framework that allows the user to 'port', 'access' or 'transfer' data between multiple platforms. This re-emphasizes the fact that the community member is the owner of the data she is creating - not the platform storing the data.
This is akin to 'number portability' in mobile carriers wherein a consumer can choose to retain the same number even as she switches from one mobile service provider to another.
A number of companies have come together to form the DataPortability.org initiative and have committed to providing transparent access to user data as and when their members want to switch. For more information, including videos of how data portability helps everyone, visit www.DataPortability.org.