Microsoft Outlook user and GTDer Scott Hanselman uses flags and search folders to clear his inbox. Scott writes:
I also try to get to ZEB (Zero Email Bounce) every day or so. This is when you "bounce" up against zero emails in your inbox... This doesn't mean that you've done all your tasks, instead it means you know what your tasks are. [...]Remember that your inbox is not storage, it's a list of what hasn't been categorized yet.
Hit the link to see the folders Scott uses to categorize his messages—in fact, his system isn't far off from my Trusted Trio.