I can imagine a web editor with some "3d space" flair. You have your HTML/JS/CSS editor in front of you, but imagine strands connecting CSS rules to the HTML elements in the preview window, which is floating slightly to your right. Or the page being previewed can even be the size of a 5-storey building which seems to be standing across the street.

For another interesting use case, how about a 3d debugger that lets you follow a program flow over multiple classes and stacks...