I'm putting another vote for the physics guys. I understand that the QM sequence may be too tangential to be included in a book about rationality, but all of the posts on "philosophy of science" that made MWI obviously true seem worth including.
Since I'm a physics major and my friends are too, the whole "philosophy of science" bit is what I'd loan out the book for (The bit on baye's law occam's razor, belief in the implied invisible, "the map is not the territory", minds as cognitive engines and such)
I guess the "here's what we're trying to do" part seems more interesting than (and should be learned before) the "here's where human minds consistently don't do that" part.
I would LOVE to see the QM sequence in there and I'd give it to my friends just for that. At the same time I suspect it may reduce the overall impact of the book. I know a lot of intelligent people (for most part those over 40) who would reject the book based on their disagreement, particularly since it is not Eleizer's field of expertise.
I'd let a rationalist with a Physics background fight that battle.
Followup to: The Most Frequently Useful Thing
What's the number one thing that goes into a book on rationality, which would make you buy a copy of that book for a friend? We can, of course, talk about all the ways that the rationality of the Distant World At Large needs to be improved. But in this case - I think the more useful data might be the Near question, "With respect to the people I actually know, what do I want to see in that book, so that I can give the book to them to explain it?"
(And again, please think of your own answer-component before reading others' comments.)