I simply had to say that this book, though certainly not perfect, is a very interesting (and even entertaining) piece which certainly gives Rawlsian liberals something to chew on. In complete contrast from what an earlier reviewer has said, this book is hardly an embarrasment to Nozick, and while he has altered his positions on some points in the book, his later work is hardly a repudiation of AS&U.
Nor, as this previous reviewer writes, is AS&U only currently of interest to Randian libertarians. This is absolutely preposterous, as Nozick actually went out of his way to dismiss Rand in subsequent work, and the forumlations of his arguments here are not Randian. They are far more Lockean. One might also mention that the book did win a National Book Award, which (to me at any rate), would seem to indicate that it is probably not your everyday Randian screed.
As a junior in college, I took a course in political philosophy at the University of Michigan, which boasts of the nation's top faculties in ethics. The introductory political philosophy course that I took there gave heavy doses of both Rawls and Nozick. People who know what they are talking about consider Nozick's book quite important in debate of contemporary political philosophy. Those who clearly don't know what they are talking about (see the 1-star review below) ... well, they simply slam the guy and the book.
In summary, well worth a read.