I have only used Neo4j for one customer project, but I experiment with it myself (I also use RDF datastores) and have used Neo4j in examples for two books I wrote. Good technology, and I am glad they are successfully transitioning from the open source community version to also making money with their enterprise version.

It is still a research thing, but I am starting to see occasional papers on inducing relations in graphs using deep learning. If this proves useful, that should help the growth of graph databases and the use of knowledge graphs.

However, as another commenter ‘hardwarsofton’ said, just using Postgres is very often all I need.