Just a thought that keeps occurring to me: recommendation systems for things like music and movies would be much more effective if they were more explicit in their data gathering. Collective filtering is amazing and incredibly powerful, and there are incredible ways to make recommendations based on the features of an item on its own--without even considering what other similar people like.
Unfortunately consumers have absolutely no access to the parameters that control their recommendation systems. When I use Netflix for example, I often find something that I will like eventually, but at no point does Netflix ask me to participate explicitly in my own recommendation process. I don't rate the movies that I watch, and I think most people don't, because I don't think they realize that the machine learning algorithms in place to help them find movies that they will love depend quite a bit on their input.
As another example, when I use Spotify radio, my mood changes during the hour or so that I am listening to the radio. The station is not designed to change with time in a way that reflects my mood, but rather to basically degrade as I start vetoing songs that I am tired of hearing. If there were a way for me to, say, move a slider that corresponds to the "songs with higher energy" data field that no doubt is being used in the algorithm that is governing my music listening, I think I would be able to help myself and Spotify out in generating better personal recommendations for myself.