VSphere is definitely a step in the right direction for those who are using VMware version 3.x and possibly the right step those who have never used VMware previously. I guess the important question at the end boils down to "What is the path of least resistance both to bring your skills up to date and to introduce or update your environment as painlessly as possible to vSphere?" To cut a long story short, Unless you have the ability to attend the vSphere course or have the time and resources to swot the technical manuals; you will have a bit of a bumpy ride ahead of you. Getting started of vSphere for those who are new to the product or those who are living with VMware day and night is definitely made a lot easier and shorter by this book. It gets you started as quickly as possible by explaining the whole concept of virtualization and its implementation using VMware ESX 4.x known as vSphere. Tips, real life examples and recommendations from someone whose job is to design, implement and support the product are everywhere in the book and offer a very valuable insight into the product.
So, Should You Get This Book?
Newbie: For a VMware Newbie, this is a very good book. You're in for a proper initiation into the virtual world of computer resources. Still, you do need to work with the product otherwise your retention for the information presented will be very very short indeed.
Seasoned: Short path to upgrade your ESX 3.x knowledge to vSphere and see what's new in ESX 4.x. Once done, the possibilities are endless, or at least you can start reading the technical manuals for more details and specifics and the multitude of presentation, White & Technical papers and plenty of high quality training video on the net and You Tube.
Seeking VCP: The book will cut your study time in half; your will get all the essential information and a few valuable tips to get your nearly ready for the big day; but again you will have no choice but to scourge through the technical manuals and examine every screen in the product to get really really comfortable before attempting the VCP 4.x exams. There is no substitute to experience.
Attended ESX Course: From previous experience, ESX course are well laid and worth every penny spent.
No doubt, this is a good enjoyable book and quiet informative. I'm reluctant to say it's a "Mastering" as that stage of knowledge requires substantial commitment to work intensively with the product hand in hand with the technical manuals before you can say you have mastered the product; but it's a tool for mastering the product.
A quick note, you will outgrow this book quickly, so you may not end up keeping it as a reference; the products technical guides from VMware are 2nd to none in their quality.
Another interesting point, between me and my colleagues in the office we purchased about 5 copies of this book; we all loved it.