The following is an email response to a customers feedback form question entered on the autodesk.com product feedback link. All feedback form submissions go to the actiual product teams. This response on CUI was very helpful and Bud said I could share his reply.
— — —
The menu system has not been updated in many years and we have been asked by many customers to be able to migrate settings between releases on upgrade. Because the old menu system is ascii base, we could not tell who created what customization. Going to an XML based menu system gives us that ability and in the future releases we will be able to migrate CUI customization forward. What we have seen with CUI is that most people that are having issues with it are not understanding the flow of how it works. We are working on making that better in the next release. For now we have animations available on the WEB Site as well as white papers that will help you get up to speed on CUI. I taught 3 courses on CUI at Autodesk University this year and talked to a lot of customers about it and how it works. The one things I heard over and over was that as you use it, you start to understand the flow. And then for many menu customization tasks, it’s simpler to use.
Let me give you some screen grabs on how to create a Flyout in CUI. It’s actually really simple compared to AutoCAD 2005 and back. I’ll also post some links to the white papers and the animations.
- Bring up CUI and expand the Toolbar node.
- Right click and add a new toolbar. I called mine Flyout Test.
- Now right click on the Flyout Test Toolbar.
- Click on New and notice you have a choice between Toolbar and Flyout. Select Flyout.
Screen Grab of the right click menu:
Screen Grab showing the Toolbar node and the properties node of the CUI: 
Now click on the Flyout to create a Flyout Toolbar. Give the Flyout a name. I called mine Filters to represent what I’m going to use it for. Then go to the Command List and select all the X,Y and Z filters. Drag then up and drop them on the Filters Toolbar.
Screen Grab of the Flyout you are creating:
Here is what it looks like after you drag the filters onto the Flyout:
Now you can OK the changes and see your new Flyout on the AutoCAD Screen.
You can also add your own custom commands or other toolbars to this new Toolbar by just dragging and dropping onto it. If you have already created custom Commands with your custom macros in it, just filter the Command list for Custom Commands and select the ones you want in your Toolbar.
Notice that I selected Notepad, Plot and Save. Then I drag then until I see the small arrow pointing at Flyout Test and I drop them. This adds these new commands to the Toolbar. 
One thing I like to do is move the CUI over to the right and click apply. Then I can actually see my toolbar to make sure I have every thing in it that I want. 
Here are the links that I talked about.
White Papers:
http://usa.autodesk.com/adsk/servlet/item?siteID=123112&id=5543397
Animations:
http://autodesk.blogs.com/between_the_lines/2005/05/autocad_2006_tu.html
Also if you would like to be involved in future decisions about what goes into AutoCAD, please go to the MyFeedback WEB Site and sign up for Beta testing and feedback project. It’s a great way to give us direct feedback while looking at the latest version of AutoCAD.
http://myfeedback.autodesk.com
Bud Schroeder
AutoCAD Test Development
Autodesk Inc.