Via Bookseller.com, though it seems now that the book in question will be published by Spiegel & Grau (Doubleday):

Jonathan Cape editor Alex Bowler has over-powered rival publishers to buy a book on superheroes by Scottish ­comics “legend” Grant Morrison, [called Supergods: Our World in the Age of the Superhero]. … [Bowler] promised Supergods would be a book “like no other”, adding: “Our world and the world of the superhero are going to be fed into the brilliant blender of Grant’s brain, so expect philosophy, anthropology, Buddhism, mad ­science, capes and punk rock.”

Supergods will be published in August 2010.