The folks at the Harvard Negotiation Project have produced a lot of books. I have found this volume the least satisfying of their works.
Perhaps this is because _Getting to Yes_ and _Getting Past No_ are so amazingly good that the level of analysis simply wasn't sustainable for a third book. Or perhaps it's I personally tend to think by analogy and had already started applying the concepts in the first two books to non-business settings. In any event, I found the concepts obvious and the discussions banal.
The quality of the later books seems to return to the same high level as GTY and GPN. For example, _Difficult Conversations_, though not strictly a book "about negotiation," is very fine, although not as easy a read as the other two.
Bottom line? Useful if you haven't figured out on your own how to apply the concepts of principled negotiation to your personal life. Otherwise, skip it.