I've long wondered about other psychological favtors that come into play as well. I wonder if each time I give a song a thumbs up, say, during radio play, they record features like day of the week, month of the year, season, the weather that day, time of day, maybe a geographic classifier like city/suburb/wilderness. These are all things that could be used to make localized, time dependent and situational recommendations. I like a lot of the 'mood' playlists Spotify offers as well, but I've used players in the past where you have to choose between very similar and highly subjective things like calm vs tranquil to populate a mood based list, and I wonder if features I mentioned could make this a more passive process on the user's part.