See this TechFlash post for some analysis
Amazon Prime is a membership program that offers customers unlimited free Two-Day Shipping with no minimum purchase requirement for only $79 a year. Millions of items are eligible, including books, home and garden products, electronics, video games, clothing, accessories and beauty products. With the introduction of Prime instant videos, free trial and paid Amazon Prime members in the U.S. now also have unlimited instant access to more than 5,000 videos.
Amazon Instant Video is a digital video service that offers customers more than 90,000 commercial-free movies and television shows to buy or rent on an a la carte basis. New-release movies are often available as soon as they are released on DVD, and many TV shows are available the day after their first broadcast. Amazon Instant Video also offers thousands of movies and TV shows in high definition. With Amazon Instant Video, customers can watch instantly on Macs, PCs, and nearly 200 Internet connected TVs, Blu-ray players, and set-top boxes. To learn more about Amazon Instant Video on your TV, visit www.amazon.com/watchontv.