I think this doesn't solve the real problem: every person will categorize a document differently and look in a different place. That's the hard part. Creating categories and uniquely identifying them is easy.
We use a similar system at work and yes, it is a problem.
For example we have categories like "customer input", "contractual", "work documents" and "delivery". Some technical specifications could go in every place at once. It is an input from the customer, and it has contractual elements, but sometime, we have to update it, and make it part of the final delivery. These often end up all over the place.
I don't think they're trying to solve this issue directly. This is intended to be used as PKM (personal knowledge management) system.
You are correct in any case that this is a hard problem and I would love to get some perspective from the author on implementing such a system org-wide.
Not sure I agree with your PKM point. It feels like it fits well for company/project structure. Reading his forum and a bit into the article it seems to advocate a "librarian" that keeps the system correctly categorized. I think he mentioned somewhere that this system doesn't fully fit PKM. I remeber some example of categorizing photos according after vacations, but running out of numbers. But I must admit I don't fully remeber the arguments.
