However, because XML is such a huge buzzword now, people are proposing (or insisting on) using it as a format at the heart of complicated applications. Where anyone would have said 'Use a database' a few years ago.
In doing so, people are losing sight of the essential beauty of the relational data model. With a RDBM, you, the programmer, have tremendous flexibility about *how* you view your data. This is a huge win inside of an application. XML forces you to commit to one specific view of your data. Yes, if that data needs to live forever and yes, if that data needs to get sent to someone else, than by all means, store it in an XML file. But if you need to *do* something with that data, you're going to be much happier with a relational db.