Facebook's platform team have shared some big numbers over the last couple of days, including that more than 400 billion Open Graph actions have been shared "back to Facebook" as of March. Facebook defines their Open Graph actions as "the high-level interactions users can perform" in a Facebook-connected app.
These actions could include a multitude of things, following, liking, listening to music, reading an article, watching a video, etc. This makes the 400 billion action number impressive, but with 1 billion+ users, you can't be that astonished. Facebook add that "on average, people choose to share their app activity" with friends over 1 billion times per day. The social network have also said that as of this month, "110 million songs, albums and radio stations have been played 40 billion times" through Facebook-integrated apps and "1.47 million books have been shared."