Passed 70-649 this morning with the following scores:
643 Applications Infrastructure - 760
642 Network Infrastructure - 887
640 Active Directory - 880
Applications Infrastructure was definitely the hardest part for me.  It was heavily focused on Terminal Services, and I shudder to think what my score would have been had I not read a few chapters of the 2008 Terminal Services Resource Kit.  Active Directory was a very short section, but I got the best score on Network Infrastructure even though I felt I did less studying on that section.  Thanks to the Second Shot promotion, I now get a discount on the 647 exam.
I took a bit different route on this exam than on previous exams.  Usually I have experience with the product and I use study guides or MSPress Training Kits to get into exam shape.  This time I really wanted to learn Server 2008 so I stayed away from training kits and study guides and used real books instead (except for Network Infrastructure where I used the Exam Cram as a quick review a couple of weeks ago).  Sometimes I read the whole book, other times just a couple of chapters, but I will list the books I think are useful and not all the books I bought.  I have been reading a bit since August, but I didn't really start focusing until October.  Reading resource kits and admin companions takes longer than training kits, but I feel I learned more and that is the ultimate goal.
Materials Used:
Introducing Windows Server 2008
Windows Server 2008 Administrator's Companion (Out of Print at Amazon)
Server 2008 Terminal Services Resource KitServer 2008 Active Directory Resource KitThe Complete Guide to Windows Server 2008 (for a non-Microsoft perspective)
MCTS 70-642 Exam Cram
Measure Up 649 Practice Exam
I got my office to buy the MSTK pack for the EA upgrade, but I didn't use it.
This is an upgrade exam from the MCSE, so the focus is on what's different in 2008 over previous versions.  I recommend starting with Introduction to Server 2008 so you know exactly what is different and you can focus your study time appropriately.
640 - Read the last 4 chapters of the AD Resource Kit and move on.  You can read chapters 14 and 15 if you have time, but you really need to read the last 4 chapters - AD LDS, AD CS, AD RMS, and ADFS.  This is an upgrade exam, and these services are the biggest changes.
642 - I used the Exam Cram as an overview and then used the big Server 2008 books to go over security, firewall, VPN and especially NPS/NAP.  There are some labs on Technet virtual labs that go over NAP and SSTP VPN.  They're short and worth the time.
643 - Know thy Terminal Services!  This seemed like a HyperV/IIS drive-by followed by a full Terminal Services invasion.  Again, this is an upgrade exam and Terminal Services has changed a great deal so expect to be grilled on it.  If you really want to ace this section, read everything but the last chapter of the TS Resource Kit.  Expect to fail if you don't at least read chapters 6 & 7.  I did not feel that the Administrator's Companion went into enough detail on these sections, but I didn't read the TS sections in The Complete Guide so I can't comment on their contents.  Stick with the Resource Kit and you will be fine.
As always, the more experience and lab time you have the better off you will be.  I'll say it again - this is an upgrade exam for 2003 MCSEs, so focus on what is new.  Don't expect 10 softball questions about NTFS permissions or other features that haven't changed.  Microsoft assumes you know it and doesn't waste time on the exam asking you about it.