Taking the example above and imagining it extended to disks and documents as opposed to topics and comments I like to think of it in terms of the real world ob

Taking the example above and imagining it extended to disks and documents as opposed to topics and comments I like to think of it in terms of the real world objects the metaphor is meant to mimic. So I think of documents the way I would pieces of paper on my desk and control panels like light switches in my house (to borrow John Siracusa's example). On the other hand, something like an address book or a filing cabinet full of tax records is not what I'm interested in organizing spatially. Instead, I'd use a purpose-built tool such as an address book application or document-oriented database. Likewise for photos or music, which lend themselves to custom database applications of their own. I'm not sure what your treemap-like graph database would be optimized for, other than disk space cleanup tools (which I have used).