Just did my 71-647 (70-649 when it comes out of beta), without preparation... I just checked some links;
Permanent Link to 70-647 Windows Server 2008, Enterprise Administrator
Erfahrungsbericht 71-647 (German)
In general, my impression is in line with what Lucas and Noxx experienced. In terms of subjects, my exam was quite a lot of GPO, File Server, Clustering in combination with SQL Server 2005 , AD DS, AD CS, AD FS.
Should I have to take this exam again, there still is a little I would look at based on today's experience. The only subjects I would be looking for are:
In general, being MCSE 2003, proper preparation for 70-649 and a bit of reading on the four topics above should be enough...
Oh, I added my remarks on 5 out of 71 questions that had some serious flaws or were just plain wrong.