That may have been the case at one point, but Spotify has used their own recommendation system for a while.

http://www.quora.com/Spotify/Pandora-radio-is-built-on-their...

I'm sad to hear this, since the Radio feature is pretty bad. I guess that means losing The Echo Nest is no big deal, though.

Rdio also uses The Echo Nest for their radio feature, and it's great. I always chalked up Spotify's radio sucking vs. Rdio's radio being so good due to Spotify having shitty integration with The Echo Nest... maybe that will change. One thing that always struck me about Spotify is that they never seemed to put a priority on anything around actual music discovery.