I have been busy lately with feature work and working on the impending release of our March CTP that will be compatible with the Feb. CTP of WinFX. However, this weekend, I got a chance to play with Interactive Designer again and came up with a simple widget. Here is the result - you need the Feb CTP of WinFX to run the sample:
The cool part was that given couple lines of framework code (for making the transparency work), you can take Interactive Designer and go wild designing the widget of your choice. This one required no code (other than a couple of trival event handlers here and there) and every line of Xaml was generated in Expression Interactive Designer.
Source can be downloaded and re-used (excluding the content) at will from here.