You brought some awesome examples. One of the best ways to get your campaign off the ground is by starting with the ideal audience. I find that I can use data to find my top customers and then make those into ambassadors, nurture those relationships, to create an epic viral campaign. Gilles de Clerck, founder of the Growth Revolution, talks about it here - https://sharesomefriends.com/blog/referral-marketing/
Dropbox was at least partially inspired by PayPal, which literally paid people money (through the PayPal system) if they got their friends to sign up. They did this because they benefited from the network effects of having large number of users- so even if half of the signups were people who just wanted the free money, the end result is a large number of people having PayPal accounts- which is a useful position for a payments company to be in.
If video advertising became more action-oriented this past year, it’s in large part due to evolving consumer behavior. UX research we at YouTube carried out in 2018 revealed that, contrary to popular belief, people aren’t always looking for a leaned-back, passive viewing experience. Actually, as we discovered, many video viewers crave something more interactive.
Furthermore, advertisers may encounter legal problems if legally required information doesn't actually display to users, even if that failure is due to technological heterogeneity.:i In the United States, the FTC has released a set of guidelines indicating that it's the advertisers' responsibility to ensure the ads display any required disclosures or disclaimers, irrespective of the users' technology.:4–8