I understand that Paramount has pitched the idea for Godfather IV in 2007 totally unrelated to the recent book. The new movie involves Vincent and flashbacks to what would have been if Sonny had lived as Padrino. Pacino is but an afterthought and Garcia and Caan would be the focus of the movie. The book's failure is responsible for the change in focus.

NOTE: I have this by NO reliable source and it is pure gossip unless I can hear otherwise from this site.

"The Godfather was a man to whom everybody came for help and never were they disappointed. He made no empty promises, nor the craven excuse that his hands were tied by more powerful forces in the world than himself. It was not necessary that he be your friend, it was not even important that you had no means with which to repay him. Only one thing was required. That you, yourself, proclaim your friendship. And then, no matter how poor or powerless the supplicant, the Godfather would take that person's troubles to his heart. He would let nothing stand in the way to a solution of that person's woe. His reward? Friendship, the respectful title 'Don' and sometimes the more affectionate salutation of 'Godfather.' Perhaps, to show respect only, never for profit, some humble gift - a gallon or homemade wine or a basket of fresh baked goods on a holiday. It was understood to proclaim that you were in his debt and that he had the right to call upon you at any time to redeem the debt by some small service." -- Mario Puzo, The Godfather (1969).