What are AirBnb's unique scaling issues other than just being a web app with tons of usage? Uber has navigation, route optimization, queuing, etc. Facebook has

What are AirBnb's unique scaling issues other than just being a web app with tons of usage? Uber has navigation, route optimization, queuing, etc. Facebook has to propagate activity our to massive and complex social network graphs. I'm not discounting the toughness of operating at Airbnb's scale, but from my limited understanding it seems like they are not solving a new problem.