Some UI objects in both Vista and OS X have 3D properties. For example, you might be able to turn a document around and see what's on the back, or look at cascaded documents from the side, which helps you select and organize them. For the most part, however, current generation UIs are profoundly 2D.

5. Minimization of icons

Icons are the central element of today's operating systems and represent folders, documents and applications in their closed state. When you click on them to open, the icon is still there, but clicking opens the item and loads it into memory. Next-generation operating systems will make items in their open state -- not their closed state represented by icons -- the central element. You'll be able to shrink or grow just about any object almost infinitely in either direction, but size will be fluid, rather than binary -- items will be shown in degrees of largeness, rather than either open or closed. Here's what a UI without icons looks like.

The combination of these elements means that the UI practically disappears. And so does the learning curve for basic use. A child will be able to walk up to a third generation PC and start playing around with it.

Does all this sound familiar? These are the five core elements of the iPhone user interface. And they do not exist together in any other major product.