Here's a demo Silverlight application that captures the application screen and uses it a couple of different ways.
You can grab the source here.
The “Swap” button uses a screen capture to create a fun transition between two different views. The “Capture Filmstrip” button starts a timer that captures the screen every second and shows a thumbnail view of it. The “Animate Background” button plays a supporting role for the “Capture Filmstrip” button; it animates the background so the filmstrip captures are different from each other even if you don’t interact with the controls. You can click on one of the captured thumbnails to save it to disk.
This article at the excellent Silverlight Show e-magazine has more details on how (and why) to do this.