When should I use the XML data type in SQL Server?

I've done a similar thing where I serialize object data to XML for storage to avoid sql server xml data type. This removes the burden of having tables, columns, and relationships in place to hold data for complex objects. The process can be helped by using a schema that the result XML conforms to, and the database tables can be used for meta information about the objects in question. In my case, expanding the database schema to accommodate the object layout would be a big task!