Mr. Nordhagen,
You stated Geographic Coordinate System (GCS) and Datum terminology could be used interchangeably, but from the references I am reading it specifically states a datum is just one part of a GCS. The three parts are an angular unit of measure, a prime meridian, and a datum. I am not trying to sharp shoot, I am trying to ensure there has not been a change to the terminology, or if this is a commonly used expression in the community?
I am still trying to come up with my own dumbed down version of what a GSC vs Projected Coordinate System (PCS) is. I thought that your explanation was pretty good, but just wanted to see about the GCS/datum comment. I provided the link below that makes a reference to this in the very first paragraph.
http://help.arcgis.com/en/arcgisdesktop/10.0/help/index.html#/What_are_geographic_coordinate_systems...
Dennis Patterson
General Dynamics
Digital Training Instructor