At Y Combinator’s annual Startup School event today, Airbnb co-founder and CTO Nate Blecharczyk demonstrated what hockey stick-like growth looks like after several years in a row. “What happens when you append five hockey sticks together? What does that look like? That’s a really big hockey stick,” Blecharczyk asked after showing the growth charts of Airbnb’s last five years in a row, followed by the overall growth in its bookings. The numbers are pretty incredible: It took four years for Airbnb to serve its first 4 million guests - a number which has grown to 9 million in the nine months since the end of last year. In the time since CEO Brian Chesky spoke at YC’s Startup School in 2010, the service has grown more than 73x, according to Blecharczyk. Get the full story at TechCrunch