So it's last.fm for books? How it that a social graph? I don't mean to discount this data entirely, but what some reads (or what music someone listens too) is

So it's last.fm for books? How it that a social graph? I don't mean to discount this data entirely, but what some reads (or what music someone listens too) is not anywhere a comprehensive picture of a user; for this reason, niche "social" services like these hypotheticals won't be able to compete with a monster like Facebook. If the service could be a Facebook app, why will users choose this new standalone network over their existing network that already has all of their friends?