Did you know you holding down cmd-option-shift when moving a selection in Acorn will repeatedly copy + move your selection? This is great if you want to change the size of some UI elements: Command-Option-Move.mov. Holding down the shift key moves it by 10px each time. Letting up on the shift key will move it by 1px each time.
And new to Acorn 2.0.2; when using the brush tool, hold down the spacebar and Acorn will draw 3x slower than it normally would. This is great if you want to be a little bit more detailed when drawing with your brush.