Today at SXSW, Facebook revealed some stats around its Open Graph action sharing as a way to entire developer to build apps on Facebook’s platform. More than a billion app activities are shared in the Facebook feed per day, and 400 billion actions have been shared in total. The most popular category is app to share is music — 110 million songs, albums and radio states have been played 40 billion times. Books is second-highest with 1.47 million books being shared and 40 million related actions. [Source: Facebook]