The Windows Server 2012 July 2013 update rollup is an important one to install on Hyper-V servers. Specifically because of this update:
2853952 Active Directory database becomes corrupted when a Windows Server 2012-based Hyper-V host server crashes
While I have been running Active Directory with no problems on Windows Server 2012, I have talked to customers who were effected by this, and AD recovery is never a fun operation to perform.
You can download this update from here: http://support.microsoft.com/kb/2855336#Kn, or you can just receive it through Windows Update. Note – there was an issue when this update was released last week that caused crashes on some systems. This issue has been corrected and an updated package has been posted.