This document discusses key metrics and challenges around Twitter's massive scale. It notes that Twitter now sees 70 million tweets per day (800 tweets per second), with 8 terabytes of data generated daily. It faces challenges in supporting real-time delivery at this scale across half the world's population, while also enabling complex queries, relevance systems, and analytics on its massive distributed graph database. The document invites the reader to follow the author on Twitter to learn more about scaling challenges.