UNIX and Linux System Administration Handbook (4th Edition)

I've been carrying this book around with me and sampling its wares for a couple of months now, but haven't had the bandwidth to write a review before this. Fear not. The wait is worth it. This is the "twentieth anniversary edition" so I imagine some fanfare went along with the book's release (though I can't swear to it). The question is, why do you want to buy this book? There's a little blurb on the book's back cover that's different than most other blurbs. Most books have quotes of praise from the authors, from readers, and from other people with an investment in the topic, but never (which is to be expected) from the competition. Remember that Prentice Hall publishes this book. Tim O'Reilly (yeah, that Tim O'Reilly) actually touts this book...publicly. It must be something. In fact, it's so good O'Reilly wrote the book's Foreword. Like a number of technical book titles that have gone the distance, UNIX and Linux System Administration Handbook has already established itself as a classic. People will buy this book just because they really liked the 3rd edition. But what's new in the 4th edition? I went looking for the answer.