Recently I have been working with an object database in particular DB4O from db4objects and I have found it to be refreshing from working with RDBMSs like SQL Server 2005. I will keep posting chunks of code as I write more spikes to get the hang of it.
http://journals.aol.co.uk/blueberryscub/rebeccas-corner/entries/2007/06/15/db4objects/1752