From Luke's interview with Eliezer:

LUKE: Well Eliezer one last question. I know you have been talking about writing a book for quite a while and a lot of people will be curious to know how that’s coming along.

ELIEZER: So, I am about to finished with the first draft. The book seems to have split into two books. One is called How to Actually Change Your Mind and it is about all the biases that stop us from changing our minds. And all these little mental skills that we invent in ourselves to prevent ourselves from changing our minds and the counter skills that you need in order to defeat this self-defeating tendency and manage to actually change your mind.

It may not sound like an important problem, but if you consider that people who win Nobel prizes typically do so for managing to change their minds only once, and many of them go on to be negatively famous for being unable to change their minds again, you can see that the vision of people being able to change their minds on a routine basis like once a week or something, is actually the terrifying Utopian vision that I am sure this book will not actually bring to pass. But, it may none the less manage to decrease some of the sand in the gears of thought.

LUKE: Well it sounds excellent to me and what’s the second book that this has become?

ELIEZER: That’s all the basics of rationality that ought to be taught in grade school and are actually just taught piece meal in various post-graduate courses.

What is truth? What is evidence? Probability is in the mind. What does it mean to say that a hypothesis is simple? How do you do induction?

Reductionism. What does it mean to be any universe where complex things are made of simple parts. Just covering all the basics really.

From John Baez's interview:

Right now my short-term goal is to write a book on rationality (tentative working title: The Art of Rationality) to explain the drop-dead basic fundamentals that, at present, no one teaches; those who are impatient will find a lot of the core material covered in these Less Wrong sequences:

• Map and territory.
• How to actually change your mind.
• Mysterious answers to mysterious questions.

though I intend to rewrite it all completely for the book so as to make it accessible to a wider audience. Then I probably need to take at least a year to study up on math, and then—though it may be an idealistic dream—I intend to plunge into the decision theory of self-modifying decision systems and never look back. (And finish the decision theory and implement it and run the AI, at which point, if all goes well, we Win.)

As far as I know, little if anything has been announced in any official capacity (release dates, publisher, etc.).