Of late there have been several Core Image based image editors released for the Mac. Scribbles does not attempt to be one of them. It is first and foremost for, well, scribbling or doodling. What makes it interesting is the very simple interface, plus the stroke rendering engine that automatically smoothes out strokes. This is particularly apparent when using the mouse to write out letters. Instead of jagged edges you get fluid lines. The interface is designed to be extremely easy to use, and accordingly the tool set is very limited. Nonetheless, there is basic 3D layers support which makes it relatively easy to get some nice effects. My sense is this would be a great drawing application for kids.
Scribbles is $19.95 and a demo is available from atebits. There's also a screencast on that same page worth checking out.