1. Startups use data in three main ways: keeping track of key metrics over time through weekly health checks, performing experiments to test different product features and marketing campaigns, and automating user communications like on-boarding emails and notifications. 2. Everyone in the organization should have access to data and use it to inform their work, whether it's testing new product features, optimizing marketing campaigns, or tracking customer support response times. 3. Viral growth relies on maximizing the viral factor K, which is the number of new users each existing user will invite over a period of time. This can be increased by optimizing the number of invites, conversion rate of those invites, and length of the viral growth