Patently Apple keeps an eye on all of the patents coming out of Cupertino, California, and they've been seeing a lot of patents for a 3D interface for Safari. This does not mean that you'll be wearing special glasses to do web browsing; instead, it describes a way in which existing Apple patents can be used in a GUI to overlap and stack windows and content.
The website describes several uses of 3D stacking to provide a different web browsing experiences. First, there's a discussion of "Rotating Titles of URLs, Emails, Documents, Apps" described in a specific patent application -- in this method, windows are exposed edge on until you wish to use them, in which case they are rotated into view.
Next, Patently Apple talks about a second patent that describes how open windows are displayed in a three dimensional browsable parade. That's tied into yet another patent describing how to present and browse items in a tilted 3D space. A possible 3D interface could include windows that you could flick through much in the way you can currently view images or file icons in Cover Flow.
As usual, none of these items may ever appear in an actual shipping Apple product, but it's fascinating to see what the minds in Cupertino are thinking.