Spotify knows what time of day users listen to certain songs, and in many cases their location, so programmers can infer what they are probably doing—studying, exercising, driving to work. Brian Whitman, an Echo Nest co-founder, told me that programmers also hope to learn more about listeners by factoring in data such as “what the weather is like, what your relationship status is now on Facebook.” (In 2011, Facebook entered into a partnership with Spotify.) He added, “We’ve cracked the nut as far as knowing as much about the music as we possibly can automatically, and we see the next frontier as knowing as much as we possibly can about the listener.”
John Seabrook's article on Spotify for The New Yorker is a good one. A lot of interesting details about the company's CEO, Daniel Ek, and the way they make deals with labels.
I remember trying Spotify many years ago with a fake UK account and telling my girlfriend that it was incredible and the future of music was going to be streaming. In the years I've spent jumping between music streaming services, I've kept an eye on Spotify and their marketing efforts, which the article doesn't mention (all my friends in Italy know what Spotify is; my mom uses it).