I don't think tags are the solution. Human beings organize stuff by lumping similar things together, by spatial relationship. It's the way the brain is designed to make sense of things on a neurological level.
Tags create a meta layer of information on top of the actual spatial organization of objects, which is hard to comprehend naturally.
The problem is we have too many virtual things to organize them spatially. It worked with the finder when each user have a few or few dozens of or maybe even a few hundred files they cared about. Now computers have millions of files, and I don't see how we can sensibly organize them spatially and still find things.
I would say that now the dominant way of finding things on a computer is not organization at all, but search. Type some words describing the thing you want to find. We've been trained by Google that we should always be able to find anything we want this way.
True, but right now search fails miserably for images. It might not, if people tagged their images better (facebook does a good job of getting people to do this), but most people don't.
Why do you say that tags can't represent the spatial organization of objects? Can't you lump similar things together, by putting them under the same tag?
Tags create a meta layer of information on top of the actual spatial organization of objects, which is hard to comprehend naturally.