Dropbox’s referral program is possibly one of the most famous cases of referral marketing done right. Almost a decade later, it’s still used in numerous case studies showcasing how referral programs can contribute to a company’s growth engine- or even be the engine itself. Let’s have a quick dive in Dropbox’s metric history: September 2008: 100K registered users December 2009: 4M registered users September 2017: 10B evaluation + 1B revenue. But, what happened between 2008 and 2010? Let's find out.