Interesting to think how Snapchat fits in this paradigm. Certainly benefits from simple Facebook-esque network effects, but it’s interesting how transient content actually provides even more fuel for engagement. The more snaps I send, the more I’ll receive since my account is surfaced in friends’ recent contacts — but I have to keep sending snaps to sustain this. And because stories disappear in 24 hours, I need to constantly both view and create new stories. Required frequency of use drives the habit.