Here's a chance to get up-to-date with db4o's big brother, VOD (Versant Object Database). This hands-on presentation by Robert Greene (Versant's VP Open Source Operations) takes a working in memory Java application and shows every step necessary to add an object database as the form of persistence. It then takes the application and makes it fault tolerant and distributed and then shows off some parallel queries. Finally, tools are used to analyze performance and show cache load optimization. All done from soup to nuts in ~45 minutes.
http://java.dzone.com/articles/distributed-object-database