The stakes are high. After just six years in operation, Airbnb has served more than 15 million guests in nearly 200 countries. In April, it was valued at $10 billion, slightly more than Hyatt Hotels. Uber, a service that matches drivers with customers in need of a ride, started in 2010 and now reportedly grosses about $20 million a week. Lyft, another ride-sharing service, began in San Francisco in 2012 and has since expanded into more than 60 U.S. cities.