Acting like we'll never get attacked is what allowed the 93, and most importantly, 9-11, incidents to occur in the first place.
Wrong, wrong, wrong!
If Americans saw a memo from their intelligence agencies saying that "Osama bin Laden determined to strike the US", and hints that hijackings will occur...Americans would not allow for it to happen. Yeah, Bush let them happen, but you can't fault Americans for that.
In this case, we have a book from some known people, and some anonymous people, who probably aren't currently involved with the CIA or FBI. We can't take it as seriously as warnings from these organizations.
What can you do about this anyways? In the case of 9/11, they could have ramped up airline security (at least on US flights, and locked their cockpit doors), and could at least arrest those they knew were going to hijack planes.
In this situation, the people and government can't do much about it. It's up to the CIA and FBI to be on top of such things.