Okay, a couple of years ago I came across a site of a concept designer who had the simple idea that the icon for the drive could reflect its health. This was back in the XP days, before Vista/7 were even showing the Free Space in their icons.
I tried finding the page I'd found years back but no luck. Here's the gist of it: The hard drive's icon would be dynamic. It would show not only how full it is but reflect its health (red/green fill) and fragmentation level (a light/heavy fog over it)
This idea has haunted me for some time and I've brainstormed how to do it but they all involve have a hundred icons stored in the exe (or the sk1llz to make/layer them on the fly)