In one of the most telling IMs of their entire correspondence (see page 62 of The Complete Timeline), Zuckerberg stated: "i kind of view you as a friend." This came up when Zuckerberg was annoyed that Greenspan made a security hole public. Greenspan handled the situation with immense professionalism, while Zuckerberg simply could not accept responsibility. Mark's friends are only entitled to the appellation when it's convenient for Mark.