Designers and the rest of us mere mortals have been clamoring about the incorporation of coverflow into everything apple. iTunes has now made full use of it, it will be a major part of the iPhone interface, and in Leopard the finder seems to be all about it.
But what is the big deal? Why has Apple based so much of its UI around it? I mean, it's pretty and all, but it really is a very difficult way to find something. Horizontal scrolling with a mouse is just difficult and slow. So why has Apple invested so much in it? I believe the answer gives us some insight into future Apple products.
Take a second look at the iPhone. OK, you've probably looked at it more than once by now, anyway. Take yet another look. This interface is the future of the mac platform. If Apple can get people used to typing on a screen, and they can use iPhone early adopters as beta testers for on-screen typing to really tweak it until it's good, then you can expect to see the iPhones's touch screen on your next macbook. What, did you think they could only make it 3.5 inches? Your next macbook will have no external buttons. Just a screen and a home/sleep/wake sensor.
So how does coverflow prove this? When you're looking again at the iPhone, notice how anyone interacts with coverflow. Flicking left and right with your fingers is extremely natural. It's even more natural than vertical scrolling. Think of it like reading a book and flipping pages. It's a very natural wrist movement. Apple introduced coverflow to iTunes way back when, but the iPhone was already in design at that point.
Face it, we are being primed for touch-sensitive tablet macs, and coverflow will be the center of the new mac OS UI.