[andrewflnr]

You tell by looking. This will utilize people's very well-developed pattern matching and spatial memory abilities. That said, it's not too hard to imagine a quick "show me where I am now" overlay, or a breadcrumb type header/footer/sidebar that shows what regions of the desktop your view is zoomed into. This is the opposite of modality: everything relevant is right in front of your face.

If an argument from authority means anything, Jef Raskin, one of the creators of the Archy system mentioned, is a large part of the reason modal UIs are Considered Harmful. If he thought ZUIs were an answer, well, you might have something mixed up.