One could argue that OS X already has a basic implementation of this with Exposé - work down at the single window level, then zoom up to the all-windows view, zoom back down, etc. It even combines with Spaces well - you can trigger both Spaces and Exposé at the same time to scour through windows on all the desktops.

There's also a feature exactly like the type of zooming described in the blog post and demoed in the flash prototype, you can turn on Zoom from the Universal Access Preference Pane, but it's something that I typically only use to check colors or graphics when designing layouts, it's not nearly as usable as Exposé + Spaces.