Over on the PAlib forums Spannernick has released an application that seeks to emulate the drawing capabilities of the Etch-a-Sketch. His homebrew application is known as Etch A Sketch DS v0.5 and it's simple to use.

After installing the file, simply use the stylus to draw. Unlike PictoChat, however, it draws like an Etch-a-Sketch, so you'll have to be careful with what you draw if you want to make something beautiful. To clear the screen, simply press the A button.

It's a nice application to while away the time with by yourself, though you may want to try PictoChat instead if you're with another DS owner. That being said, feel free to give it a try.