If you are using Configuration Manager 2012 to manage Mac Clients, and are running Mac OS X version 10.9.3, here's an interesting problem for you.
The default hardware inventory for Mac PCs is to inventory video controllers. If you leave this setting at its default, the client installed on the computer will just stop working. I'm sure a fix will be forthcoming, but for now the workaround is to simply go into the Client Settings in the Administration workspace and uncheck the box for Video Controller in Hardware Inventory.
If you need instructions on where to locate this setting, drop out to THIS link.
The workaround can be performed before or after the problem occurs. For any Mac OS X version, the computer will no longer be inventoried, but for Mac OS X version 10.9.3 computers, they will stop receiving policy settings completely because they will cease connecting to the Management Point.