With so much work being put into JavaScript Engines and competition building up between the big three(TraceMonkey, V8, and SquirrelFish) running a full blown Cappuccino, SproutCore, or any AJAX intensive app will be very light on memory usage and efficient on your resources. This JS engine competition will mostly affect the closed source Adobe’s Flex, AIR and Microsoft’s Silverlight since they can’t seem to get enough of your memory and keep crashing your browser. Closed and proprietary web frameworks have only one place in the world, and that is in the cemetery.