Articles
This behavior enabled you the Aero glass effect. Just attach it to a window. To have it work the Windows version have to be Windows Vista or later and the Aero have to be enabled.

Usage
<Window x:Class="DW.Interactivity.Demo.GlassWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:Interactivity="http://schemas.my-libraries.de/wpf/interactivity"
Interactivity:WindowGlassBehavior.HasGlassEffect="True"
Title="And It Will Be Glass"
Height="300"
Width="300">
<Grid>
</Grid>
</Window>
Note
This control needs the DW.SharpTools.