It's easy to dismiss a new database technology as irrelevant because of the dominance of the RDBMS, but you should really learn more about it and when it is appropriate and when it's not. It's not going to replace relational, and isn't intended to. Here's a few links where you can learn more beyond what's available on Ronald Bourret's site mentioned in the original post.
The XML:DB Initiative
The dbXML Project (open source native XML database) Soon to become an Apache XML project named Xindice
eXist (another open source native XML database)
My blog on the subject.