Here is my attempt to create a control that contains some animations and could be used to give the XBox 'ring of light' effect using EID. I did it by creating a new template for a control and adding a timeline to the control template that would start on the Control's Loaded event. Then I template bound some properties like background and foreground of the control so that you can change them and you are done.
I've attached a resource dictionary that has the template for the control, to use it in your app here are the steps you have to do in Interactive Designer:

1. Add a Project Item and select the resource dictionary ("RingOfLightControl.xaml")
2. From the resource palette click on the button that says "Link to resources" and select the resource dictionary
3. Then just instantiate a couple of Controls (of type Control) from the Library palette and apply the template (Right click on the control | Edit Template | Apply Resource and select RingOfLightTemplate

In the app shown in the picture I instantiated three controls of different sizes to give a more dramatic effect

 
Here are the steps to creating this template in Interactive Designer:

1. File | New | Resource Dictionary
2. In the resources palette click on Link to resources and select the dictionary you just added
3. In the scene now create a control (of type Control) from the library palette
4. Right click on the control | Edit Template | Create Empty Template
5. In the resource creation dialog slect the radio button that says "Other document" and select the resource diationary you created
6. Add a grid into the template using the library palette
7. Draw some ellipses into the grid
8. Now create a timeline
9. Create some scale animation and opacity animation for the ellipse at different times
10. Select the template node (may called "value")
11. In the timeline properties palette add a trigger, the trigger should look like [TargetElement][Loaded][Begin]

At this point you are done with the animation inside the template, some other details you can add

1. Switch back to the None tab in the timeline
2. Select the Grid and from the properties palette click on background | Template Binding | Background (this will add a template binding so that when you change the background property of the control it'll get reflected on the grid)
3. Do the same thing for each ellipse you created but the template binding should be done with the property foreground.

Now you can switch back to the scene and create many controls and re-use this template