Low-hanging in the following sense: the premise - I tell you what I like, you tell me what else I might like - is compelling for the consumer, therefore, input

Low-hanging in the following sense: the premise - I tell you what I like, you tell me what else I might like - is compelling for the consumer, therefore, input is not the limiting factor. Moreover, recommender systems at such massive companies must be particularly amenable to A/B testing to help profile their customers more accurately. Finally, performance metrics are straightforward and easy to calculate.