I have been looking at ways to optimize world._arrange when there are a large number of items in the world. For each item that world._arrange repositions, it raises a bounds-change event on the tiledImage that calls world._figureSizes, which loops through every item in the world and performs some fairly hefty calculations. For a world with above 1000 items, this was getting to be expensive. By canceling all of the bounds-change events in world._arrange and calling _figureSizes only once at the end of the loop, I changed the time it took to rearrange 1000 images from > 2 seconds to almost instantaneous. Then by reducing calls to world._arrange in addTiledImage, I cut the time it took to add 1000 items to the world by half. I'm eager to make these optimizations for our app, but I suppose that I can't just cancel all the bounds-change events in world._arrange, especially if I want to push this change. Any comments? Maybe _figureSizes could be called based on an internal state?