(UPDATED) The Echo Nest and Spotify have integrated APIs so that Spotify app developers can tap into The Echo Nest's music intelligence platform. The Echo Nest already powered Spotify radio, but none of its official apps. Some third-party apps like SpotON Radio and Echofi have already been utilizing the both APIs.
Currently no official Spotify apps are utilizing The Echo Nest API, but the company envisions a variety of applications: As songs play, an app could display lyrics, Tweets and Facebook updates from the artists being played alongside ticket offers. A radio app could pair bands with reviews, bios, and the option to branch off to a new station based on any song or artist.