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.

Cheers,
Ben