1) The document discusses lessons learned from using agile development practices like multiple pushes per day and extensive customer development at Meetup. It emphasizes giving developers direct access to customers and substituting frequency for precision to get feedback.
2) Meetup conducts many usability sessions per year at a low cost to get direct feedback from customers on experiments. They test multiple times per week and recruit participants from their community.
3) The key lessons are to look for problems, minimize costs but trade money for time, have discussions, launch and learn quickly, and expect failure so you can experiment and double down on promising ideas.