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Pie menus are awesome. Specially when each item can be executed with gestures. I use blender and it has an awesome implementation of Pie menus. And also highly customizable. The idea is instead memorizing a bunch of keyboard shortcuts, you can just create pie menus with 8 items and call it with a hotkey you assign to it. So instead of one hotkey invoking one command, you can get 7 more with gesture based pie menus. With gestures, it becomes muscle memory pretty easily. This also minimizes the use of the UI, meaning you don't have to move your stylus to the corners of the screen and just stay inside the canvas. Here's a screenshot of a blender pie menu for example:
http://imgur.com/mlPJREM

In my opinion PIE menus could replace toolbars, but t will have search option.