Sketches : $4.99
Line Types (ie softness of edge, transparency): One hard-edged line, 3 levels of opacity.
Line Sizes: Slider
Drawing Method: Draw with finger, no offset, no tilt effects.
Drawing Colors: 24 presets, no color picker.
Backgrounds: 24 preset background colors (no color picker) plus can use camera, maps, your photo library, website screen shots, and included library of overlays such as graph or note paper. You can change the background at any time without affecting your drawing, which is an overlay. This means, for instance, that you can work off a photo, and then eliminate the photo from the final drawing.
Shapes and Clip Art: Included library of re-sizable geometric and clip-art shapes including speech bubbles.
Paper Size & Adjustability: One paper size, size of screen. Paper cannot be moved away from iPod Touch/iPhone edge or tilted.
Zoom: Have to use unintuitive zoom icon; pinching gets you last chosen shape, clipart, or text.
Undo/Redo: Apparently unlimited undo-s, no re-do-s.
Eraser: Yes. Correctly erases down to selected background image/color, which remains unchanged.
Clear Screen: By shaking (a la etch-a-sketch of old). No option to turn this off or have a dialog box. Cannot undo. Do not move the device quickly when putting it down or you may unintentionally clear your drawing!
Text: 3 fonts, 24 preset colors (choose color before going into font menu), can't move text after initial placement.
Hide Menus/Full Screen: Double-tap.
Save Options: Can keep 30 images in program library, save .jpg to photo library, send directly to twitter, email picture or share on web. Approximately 4" X 5.5" 72 dpi when saved to Photo Library.
Appropriate for: Everyone, from kids to experienced artists.
Here's the beginning of the Big Chart comparing all the art programs I've reviewed so far.