I agree completely about Graph DB's. I used a third party Graph database that was schema heavy on Nodes and edges and it was amazing for mapping business processes as the customers can actually understand the data model and we did not need any DBA's. I wrote several custom enterprise systems based on this graph backend that were very successful in their deployment and upkeep.

The company that has this DB never sold it on its own and its only available with their $$$$ CAD / CAM / 3D / PDM / PLM software packages used by the big guys (E.g. Boeing, Honeywell ...)