Zipcar has experienced remarkable growth through product power, strong branding, and network effects. Zipcar offers convenient car sharing that allows members hourly access to vehicles without long-term ownership commitments. Since launching in 2000, Zipcar has grown to over 325,000 members and 6,500 vehicles across North America. This growth is driven by compelling value to customers, network effects as vehicle locations increase, and economies of scale that lower costs. While Zipcar maintains leadership through its size and network, future challenges include competition, external factors like gas prices, and potentially becoming a public company.