Permissions needed for Reparent Master Detail in Custom Objects
The ability to allow reparenting of children in Master Detail objects was a welcome addition in Summer '12.
However, it seems that you only have an ON/OFF setting for this and no control on who can do it.
What is needed for a complete implementation is the ability to selectively enable that capability either by a Profie/PersissionSet/Role and/or a Record Type.
In my use case, I would only want to allow certain groups of users to reparent certain detail records of a certain record type.
The addition of the permission side of this would really round out this capability and make it enterprise strength.