I've got a nice O'Reilly book on Kerberos from our library, but it was last updated in 2003. I'm pretty sure there have been changes and improvements since then, especially with AD 2008. Are there newer books on Kerberos?
Couple seconds on Google after I left my comment above: http://technet.microsoft.com/en-us/library/cc749438%28WS.10%29.aspx
So, in other words, not much. Couple of differences in some implementation details, but Kerberos is still Kerberos, and will continue to be.
Just to add to the knowledge pool there are some changes of default behaviour such as DES support is not on in Windows Server 2008 R2 onwards. See http://technet.microsoft.com/en-us/library/dd560670%28WS.10%29.aspx
The answer's here will really depends on people's definition of "changes and enhancements". But books wise I use the old Oreilly kerberos book and look up details on 3rd party implementations on the net as applicable (e.g. Linux vedors for details on setting up KDC etc). Use your favorite search engine or vendor support pages depending on the Kerberos implementation if its not AD.
Would this video be something you'd find useful? http://channel9.msdn.com/Blogs/Darryl/Active-Directory-System-and-Security-Changes-in-Windows-2008-R2 Doesn't focus exclusively on Kerberos but does include the detail.