It occurred to me when Gmail used it. Many other sites/products/services were using this same concept, albeit with different names.
It made me wonder, why at all have folders? Why not have just tags? How about a world without folders?
Well, if you think I am fantasizing then you should look at evidence that people are moving in this direction.
2 years down the line, you might see that “Folders are history”! But the question is what will replace them? Is it tags? Well, in its present form, tags are not quite a replacement to folders. While tags have several advantages like automatic rule application, there are some disadvantages of tagging compared to folders. One that I can describe right-off is “Context awareness”.
Suppose I tag a file by name “Project” does it mean it is MY project, or does it mean SOMEONE ELSE'S project or does it mean PROJECT RESOURCES? In folders, it is possible to give a context to the data, while tags in their present form, will not help us here.
A good solution is to have the best of both worlds. The concept of tag clusters would probably be what would actually replace folders. It is not yet unclear how tag clusters would look, so it would be early to comment on it, but you can expect something soon!