i think apple is going to implement their equivalent of compiz or beryl. that stuff on linux is pretty cool, but is a pain in the butt to implement. those are some cool features that i bet they are going to implement in leopard. 3D desktops are going to be just the beginning.
Everything that is useful about compiz and beryl (from what I've seen--updating windows in dock, growing icons, expose-like features, animated windows and app launching, overlaid app switcher) is already in Tiger and much of it was in Jaguar and Panther too. Even some of the useless compiz and beryl stuff (rotating screen cubes, running a screensaver in the background, transparency, morphing UI elements, elements fading-in and out etc.) are old-hat on OS X.
But really... are you suggesting that Apple's big secret feature that they've kept us all on the edge of our seats over is windows that wiggle when you drag 'em?