I recently passed the 70-649 exam with good scores and this book, 70-648/70-649 Transitioning Your MCSA/MCSE to Windows Server 2008 Trainng Kit, was very helpful. However the text of this book alone, nor any other, most likely would not allow one to pass the 70-649 exam that covers a lot of territory via 3 in 1 exam. But if you have several hours [let's say over 100] minimum hands on experience with Windows 2008 exploring it's capabilities and developing expertise for, either on the job or in your training lab, including Active Directory and Roles/Features covered by the exam and remember most of what you learned obtaining your MCSE 2003 you are well on your way to passing the 70-649.
The labs in the book were helpful if you do not have hands on with the topic or want more in depth as were the URL links to additional info sources if you feel you want more detail as configuration info in some cases was sparse BUT keep in mind that there are entire dedicated books covering topics on most of the chapters in this book . Some of the topics such as ADFS and ADRM are very complicated. I did not do the labs in total for those, other then installing the roles and configuring them as much as I could, but read through them until I understood what was being accomplished. The questions on the exam for those topics did not expect you to know configuration in great detail but you need to know in general what they are used for, high level how they work, the flow of the processes, and how authentication is accomplished.
The exam focuses heavily on what is new with Windows 2008 and assumes you have retained your MCSE 2003 knowledge about networking, DNS, Group Policy, Active Directory, forests, global catalog server, trusts, sites, replication, etc. If not I suggest you also study with the Microsoft Press books for 70-640 and 70-642 or if you want some extra reinforcement on those topics.
I found that IPV6 in the book to be a bit overwhelming as in "do I really need to know how to subnet IPV6 and all the interim solutions such as Toredo". There were no hard IPV6 questions on the exam and I believe I had only 1 question. Knowing basics such as what is the IPV6 equivalent of an IPV4 private/public/APIPA address and how to troubleshoot IPV6 connectivity using basically same tools you use for IPV4.
I found the chapter on IIS7 very helpful in learning the new management interface, which has been totaly revamped, and new features such as management delegation and additional configuration for application pools such as recycling, and was all that was needed for the exam. There were also plenty of command line examples for IIS7 and other topics throughout the book and you will see a fair amount of those on the exam where you need to choose the correct command for a task.
The exam places great emphasis on security including what remote solutions need only port 443 TCP open in the firewall, certificates needed for SSL and implementing client trust for such certificates, solutions for revoked certificates, which authentication methods use certificates, CA types and hierarchy to use, distributing certificates to internal and external computers/users, Terminal Services, minimizing risk of having a domain controller in a branch office, and when to use ipsec/EFS/Bit Locker for a stated scenario and which one accomplishes the task. I felt the book did a good job covering those topics.
In addition to this book it would be well worth your while to study Microsoft documentation on what is new in Windows 2008, and individual what is new papers such as for Terminal Services. I felt that I easily got my moneys worth with this study guide.
EDIT 09/05/09: I recently completed my MCITP for Server Administrator and Enterprise Administrator. As the Microsoft Press books mention using Hyper-V to create virtual machines was extremely helpful in my learning process. I found that the ASRock A780GXE mainboard [around $80] with the latest bios update and using a AMD Phenom II quad core processor worked great for Hyper-V and has 4 RAM sockets. Don't assume any modern mainboard or processor will support Hyper-V. Hyper-V is easy to learn. Just remember to install the Hyper-V Integration Services on any guest OS you install right after the install to get networking and the mouse to work correctly! I believe you also need SP2 for W2003 and SP3 for XP for Integrations Services to install.