If you're working on Open XML solutions that use Word 2007 content controls and bind them to nodes in your custom XML data part, then you need this tool. It provides a simple graphical view of the content controls and custom XML nodes in a document, and you can bind a node to a control by simple drag&drop operations. Click on the screen shot here to see how it works.
It's a great way to manually create a data-bound document, and it's also a good developer tool for learning about the markup you need for binding controls to data. You can generate well-formed data-binding markup with a few clicks, then look at how it works and use the same markup in your custom solution as needed.
The tool, developed by Microsoft's Matt Scott, is available as a Codeplex project, and there's also a video on Channel 9 where Matt goes through the design and development of the tool and demonstrates its use.