Url: http://wilderminds.blob.core.windows.net/downloads/wpfesample.gadget

In response to a question on MSDN, I crufted up a really simple SideBar gadget for Vista using WPF/E as the user interface.  (It just shows a simple animation when first added to the bar).  SideBar (and perhaps Live) Gadgets are likely to be a fun place to use WPF/E.  You can download and install it here (assuming you already have WPF/E runtime installed:

WPFE Sample Gadget