What are some good resources for learning about document oriented databases? I'm interested in learning about NoSQL databases and I decided to start with document oriented databases.  What are some good resources to learn the concepts and good design of this type of database?
Here's a good article comparing document oriented databases:

http://www.mikeperham.com/2009/09/01/comparing-document-oriented-databases/

and here's a good article about designing document oriented databases:

http://ayende.com/Blog/archive/2009/03/08/designing-a-document-database.aspx