Pretty cool app but it seriously needs a undo button if you make a mistake when using the brush tool to erase or change opacity levels. For example. Try re-creating the soccer image that is shown in the App Store. The artist must have spent hours on that image but sells the app as Instant, quick, simple edits. I have spent a long time brushing away portions of the graphic only to slip with a finger and cut out part of the wrong area. All you can do is delete the graphic and start over from scratch. Not so simple after all.