Today the Netflix user experience of movies is 80% movie and 20% PC. The movie experience is all fun. The PC experience is somewhat fun if you're a technologist but rating movies and building queues isn't most peoples idea of fun. What if you could continue to pull the user experience away from the computer and still provide the same value?
The idea is to use the evelope not only as a mechanism to return movies but also as a feedback device. At the very core you could allow users to rate movies by scratching or peeling off stars. This would make it easier for the user to give the system meta-data without having to pull open a computer and login. The idea could be extended for adding movies to your list of things to watch... "If you liked this movie you may also like... please check the box to add them." (The longer your list the more likely you are to stay with Netflix)
A lot of companies assume that the best design has to be on the computer. This isn't true; sometimes the best user experience can be with paper where your interface is as simple as a pencil or even your finger nail.