Dropbox’s referral program is often cited above any other program out there. In fact, many businesses today refer to Dropbox’s program when explaining what they want in a program. This is probably because they were able to double their growth every 3 months. In fact, their users sent 2.3 million referrals in just one month. Talk about an insane growth hack! In fact, their referral program has allowed them to forgo traditional ad spending, and save by offering free product/space.