XML: Can I use it as a database?

A question popped up, that can (and should) we store slightly structured data in XML? For example: results of measurements that do not have any structure except timestamps and named columns.

Well, my opinion matches with this book's ideology:

XML is not a database. It was never meant to be a database. It is never going to be a database. Relational databases are proven technology with more than 20 years of implementation experience. They are solid, stable, useful products. They are not going away. XML is a very useful technology for moving data between different databases or between databases and other programs. However, it is not itself a database. Don't use it like one.

The important point here that you must grasp is, that XML is an encoding. It is a data exchange format, not a data storage format.