A couple of people recently pointed out that our documentation isn't very clear on what data types are available in the Content Pipeline, and the relationships between the Content DOM object model produced by the importers, the converted types output by the processors, and the types you load into your game at runtime.
So I put together this diagram:
(2009
edit: see
here for a more recent version of the diagram)
If all goes well this should make it into the next version of our documentation.