If you were trying to find a physical copy of an important tax related letter, would you prefer to search for it in a folder dedicated to tax document from that year or from a room filled with every single piece of paper that you have ever received by mail in your life?

A pure tag system only works for small libraries, it requires far more discipline by properly tagging every single file, it does not scale and it does not work well when you collaborate with other people. It works well in situation where you can automate the tagging (eg. a collection of pirated moves) but is pure garbage for normal files that you typically use.

It's a lot easier to tell people to place pictures of karl in the "karl" folder than it is to make sure that every single picture gets properly tagged with the word "karl". I can imagine hundreds of different scenarios where it gets tagged slightly wrong. Typos won't be easy to fix because they will simply not show up in the search when you type it. How many files with "K arl", "Carl" or " karrl" are there? no one will know.

There seems to be a lot of confusion here about Didget's tagging system. It is not meant to replace the file hierarchy, but to supplement it. With Didgets you can still organize all your files in a plain old folder hierarchy without tagging everything. Tags just provide a secondary way to search for things. So you can still stick all your photos of Karl in a folder named 'Karl' if you like.