Now that you've got Beta 2, you can download and open RxDemo.xlsm, a new file format document that uses RibbonX and works on Beta 2.
If you haven't changed your Macro security settings from the default, you'll receive a security alert. If you trust the document, click "Enable Content..." After carefully reading the ensuing dialog box, select "Enable this content." If everything worked, you can now click around on the custom controls. Notice the items added to the Office Menu, the custom "RibbonX" tab that can be made visible on from the add-ins tab, and the various controls that you should recognize from previous blog posts.
Take a look at the code behind the buttons in VBA, and if you want to look at the markup behind the document, I suggest you try out the Custom UI editing tool, a tool that lets you insert and edit images and the customUI part in new file format documents. There are some comments in the code as well as a number of explanatory super tooltips in this sample, so take a look and enjoy!