From JRuby Conf 2012: The object database never became a huge success despite some real benefits like no impedance mismatch, no need for a complex or leaky ORM layer and great performance (e.g. no slow JOIN operations). A graph database has similar advantages but not the same disadvantages since it avoids coupling the database with a programming language. Instead, it uses the simple language of a graph (node, relationship and properties) for interaction with the database.
There are many problems which, really, only a graph database can solve properly. We'll show you the real world challenge, transposing from whiteboard to graph database using Neo4j running in Rails.
If your database cause you trouble because you need to persist or query data with many relationships between entities or if you're just curious why we believe graph databases are the next big thing then this talk is for you.