The graph squad at Spotify has been tasked with creating the best music graph in the world. Organizing musical data is a perfect use case for a graph database, and Spotify is experimenting with Neo4j, Giraph and Titan to help them improve a music organization system that currently has no graph database, but instead has a Hadoop map/reduce-based Graph representation.
Here are some slides that Spotify recently showed at a recent meet up.
And here is Peter Neubauer's presentation slides from the same meetup. Peter is a Neo4j evangelist.
This presentation notes a useful tool that can be used to export data from a RDBMS to a graph database through CSV files.
It looks like Spotify is looking hard for graph specialists.