We've been working with the Neo team for over a year now and have been very happy. We model scholarly artifacts and their relationships, which is spot on for a graph db, and run recommendation algorithms over the network.
If you are already working in Java, I think that modeling using Neo4j is very straight forward and it has the flattest / fastest performance for R/W of any other solutions we tried.
To be honest, I have a hard time not thinking in terms of a Graph/Network because it's so much easier than designing convoluted table structures to hold object properties and relationships.
That being said, we do store some information in MySQL simply because it's easier for the Business side to run quick SQL queries against. To perform the same functions with Neo we would need to write code that we simply don't have the bandwidth for right now. As soon as we do though, I'm moving all that data to Neo!
Good luck.
