Never save state or pause an Active Directory Domain Controller.

You should always shut down virtual Domain Controllers properly to avoid replication errors. Pausing a Domain Controller for a long period of time before resuming it can interfere with timely replication. If you do pause the domain controller for a long time, replication may stop and cause lingering objects.

Backup and restore Domain Controllers the right way!

Only use the standard way to backup and restore Active Directory Domain Controller, since the default checks of Active Directory consistency will only be performed when the Domain Controller is aware of a restore.

Using imaging solutions like Symantec Ghost  and Acronis TrueImage  seem like smarter backup and restore solutions, but they are imaging solutions (in contrast to proper backup and restore solutions). Restoring an image of a Domain Controller may cause an Update Sequence Numbers (USN) rollback situation to occur, which may lead to replication problems and other undesired effects. More information is available here.

Like shutting down a virtual Domain Controller, and start up a version of from a while back, you want to avoid improperly using imaging solutions.

To avoid USN Rollback and Invocation ID problems but still using imaging solutions or even copying back old versions of a virtual disk file (which is a big NO-NO), be sure to check out this post on Backing up and restoring Active Directory in this unsupported manner.