Graph databases like Neo4j are gaining popularity nowadays, with initiatives like the Facebook Graph API. To mash up data from Facebook with local data in a graph database, you can use the Facebook Graph API to fetch information about friends and movies liked by those friends, then connect this with IMDB data stored locally in a Neo4j graph database. The code uses Sinatra and WEBrick to expose the Neo4j model over the Graph API, allowing for easy searching of actors or movies based on their names. With indexes added to the model, performing searches becomes straightforward. By using a graph database, you can perform more advanced operations like finding shortest paths, routing with A*, modeling complex domains, and whatnot. The example source code is available for download, along with a free copy of O'Reilly's Graph Databases ebook.