Nineteen, from The Aquabats to Pedro the Lion via Nirvana: http://labs.echonest.com/SixDegrees/?start=the+aquabats&...
And 23 steps from Kevin Barnes to Goldy McJohn: http://labs.echonest.com/SixDegrees/index?start=kevin+barnes...
Just a nitpick, not meant to detract from the geeky awesomness of the project.