tranglos says (somewhere on DC) that he finds it necessary to have the hierarchical tree, that (from memory) he's uncomfortable leaving organisation solely to tags. I'm not sure. I don't use tags religiously and wouldn't want a system that enforced them, but I do sometimes add words to a note so it contains the form of words I'm most likely to use myself.
That is why tags are 'ok' for personal use not for something blog posts. You may be able to train your own mind to make tags intuitive and meaningful for you. I find I use them sometimes but I think the best approach is to make the title of a node, note, etc. meaningful and give clues as to contents. One thing I like about All My Organizer for example is that you can see previews of child nodes/'folders' contents when a parent is selected. I believe Evernote is the same (?)
To be a devil's advocate, this is why tags are bad for personal use.
The average group will always have data that are less information and more data. This is because information is managed separately and information attributed activity is moved by the groups' philosophy/goals/mission/duty. No one really cares about the end result of the data and no one is affected by it because the mission goals are about contributing to the group, not contributing to the individual needs above those of the group.
In comparison, personal often comes down to individual. If you want to buy an apple for health reasons and you tagged the healthy tag, you're training your mind to always register healthy when you buy an Apple and the more you use that intuition, the less you will ever try to explore the unhealthiness of an Apple. In short, it's bias fulfilment.
The difficult part is in the question of how much harm it does.
Certainly trees and folders also have their conceptual limitations but here's the thing: they don't pretend
. Tags pretend the brain. It has a verifiable effect that can immediately be experienced by the recipient as soon as they got "their" tagtuition.
I don't mean to be a tag demonologist, certainly tags are not evil. I'm just making a devil's advocate case for the possibility that tags may be like TV ads. Also how intuition depends on data we surround ourselves with. If people as smart as scientists and economists can self-manipulate their idea which then demolish and creates a wrong paradigm shift in their theories (sometimes to their entire lifetime and beyond depending on how influential their works become), so too and especially, can personal information using tags worsen the bias of intuition.
As far as proof, I don't have any strongly backed ones. I don't even know if there's an official name to it but if you notice many of the "software hackers" of these tag based products: many who often try to create templates for their tags via the use of official names for their tags, many if not all tend to have worse sets than the average folder names.
For example, the average My Documents, Music, Downloads folder in OSes are extremely bad, bland and many times redundant. What I mean by this is that the Music folder is rarely used, the My Documents punishes the computer newbie who thinks he has to save his documents in that folder, there's no immediate reminder for backups, manuals, etc. in the same folder...but at least it's more nuanced than the average tag sets
There's an "intuition booster" of Work, Fun, Web. It barely registers an effect on the person but at least it's there so far as information concept is concerned.
The only information concept that tags often boost are find and it's not even because of the tags but because there's a search bar.
Now try to turn a nuanced intuitive information data that's in a folder into a tag and you'll feel a slight tug out of your intuition like something's micro wrong. It's at this point that the first problematic data switches from foldertag to tags entirely data. Conceptually foldertags only work as a dumbing down of tags to begin with. Comparatively, a propaganda ad that doesn't register as propaganda in your head or registers a propaganda with a positive message in your head will seem less evil than a normal TV ad even if it has every signs of being a propaganda and you know it consciously
The harm here (guessingly) is not that it dumbs down the brain but the brain has to reserve space for the intuition to use itself up for registering the tags for information finding that once you have the actual data you no longer have the chance to utilize that data intuitively outside of how you belittled that data. Fitness is no longer a tag for the dictionary word fitness, it's a tag for looking good, diet, slim waist. Forget survival. Forget the dictionary. It's about being socially attractive in public and long term, it's about being vulnerable to unhealthy fitness products sold in the market. That's IMO the conceptual difference between words besides a note and a tag. One can still register as an icon to the brain despite being a word and one has to register as a set of affirmation like words to the brain despite being a tag that no longer has to register consciously as a word and is intuitively just a data finder markup.