I agree that thumbs up/thumbs down is probably better to encode appreciation than a 0-5 scale. But for building a recommendations engine a single bit of information is not enough. If I and everyone else flags shows we are not interested in viewing 'thumbs down', then all shows end up with terrible ratings. Similarly 'thumbs down' for a great movie, but seen it already thanks so stop screaming it at me. Thumbs up and Thumbs down is certainly not all the data you need, as is demonstrated by Netflix as it stands today.