See how simple is to create a great user interface for your WPF or Silverlight application. You can simply use almost any vector drawing application (Adobe Illustrator, Corel Draw, Inkscape, Visio, Autocad, Excel, Word, etc.) and then with the ViewerSvg or Paste2Xaml convert the drawing into XAML. Or even simpler, you can use one of the thousands vector images that are already available on the internet - see links.
There are also samples that demonstrates the power of vector images and how simple is to create a great effects with them.