I have been using this book for studying the 70-621 exam (instead of the 70-620) since there weren't any books at the time for the 70-621. I have already been deploying Vista Business & Ultimate in our work domain after using Business & Enterprise at home (Technet Subscription was a really good idea).
I thought I learned quite a bit from the hands on, but I was pleasantly surprised how much this book covered in great detail. I almost always chunk the CD in the back of most books but the authors did a superb job on this CD. Excellent chapter tests of 20 questions each and two bonus sets of 50 questions each. Only problem I had was the WinSim when it showed a Movie section. I didn't get any sound but I wasn't sure I was suppose to, but either sub titles or sound informing me what tasks it wanted to take would have been helpful as it plays a little quick, so you have to replay it a few times to figure out what the scenario was about. Flashcards - I generally HATE flashcards, but this was fantastic, it didn't bore the heck out of me like 99% of them do.
Of course, the whole book is on the cd as well and I found I like reading it better than lugging around that heavy book since I can enlarge the print for easier reading.
Of course it helps to know the background of a couple of the guys (authors) who helped write this book - Michael Aldridge and Josh Evitt. They used to work for Transcender and I met Michael after he left there and have had lunch with him on a few occasions. Really good people and always willing to help/advise people on their careers and certifications (see certcities.com & mcmcse.com). Michael and Josh now currently work for Boson. Looking forward to buying products they produce for them as I know it'll be good.
For the Exam 70-620, I don't think you can do any better than this book. It's just plain easy reading (Sybex has always been good about that style) and straightforward and I almost maxed the client section of the 70-621 (just need more work on the enterprise section now). Good luck with your 70-620 exam, but with this book - you won't really need luck, just some study time.