Same Script, Different Cast: How Social Networking Can Learn From E-mail

Already, Facebook uses a combination of implicit and explicit user feedback to build a reputation for applications and decide how many of its news feed notifications actually show up for users. Just because you send a notification to a user’s mini-feed doesn’t mean that all of his or her friends will see it. Facebook looks at how many active users subscribe to your application and how many users block your messages to determine how many messages they’ll let you deliver tomorrow.