First of all, as you can see in the image above (click to enlarge), the first bullet point is "The integration of Facebook makes viral seeding easier!" The first screenshot is Facebook mobile on an iPhone, and the Facebook logo has a nice little area dedicated to itself in the bottom right corner, right below a same-size Spotify logo.
Secondly, in a second slide, Facebook is mentioned in two of the seven points answering the question "Why will Spotify be a success in the US?" Here they are:
Unique: No other product exists like Spotify in the US. Nobody does free, on-demand, radio, MP3 retail, Facebook and iPod integration and subscription together.
Spotify Social is already integrated to help spread the word. 150m Facebook users will start to see music on their feeds. One click and they can have Spotify.
It's pretty clear that Spotify plans to play up its Facebook integration right from the very start. Spotify is also telling advertisers that they'll be able to use Spotify to build "music apps" on their own sites and on Facebook pages.
Spotify is projecting that the service will have 50 million US users in its first year of operation. That number is ridiculously high: Spotify only passed 1 million subscribers in Europe in March 2011. Facebook already has a deep integration with Spotify in Europe, but it appears that Spotify is expecting much bigger results in the US. Maybe this has something to do with what we've been hearing about Facebook's upcoming music service?
Yesterday, we learned about a new Facebook service related to music, possibly referred to internally as "vibes." Mention of the new service was found in the code of the installer for Facebook's recently released Video Calling service.
Last month, a rumor suggested that Facebook was working with multiple companies to offer music services and applications. The suggested name was simply Facebook Music. In the left-hand column, where Facebook lists Photos, Friends, Places, Groups, Deals, Pages, and Games, a new tab called Music will be added. It will show up if a user has listened to music with one of Facebook's partner music services. There will even reportedly be Music Notifications, Recommended Songs, Top Songs from friends, Top Albums from friends with cover art, Recent listens from your friends, and a persistent Play/Pause button added to the bottom of Facebook where you currently have the chat icon.