I wasn't intending to revive the debate (I withdraw the Neanderthal remark), but thanks for the comments. I would like Evernote to add another level, so I gave my 2c. Like I said, limiting the hierarchy forces you to be organised, but I think they have got the wrong number of levels.
Putting things in a notebook, then searching by tag(s) to find the subgroups is unworkable, because I can't remember every tag. I use Evernote for almost everything in my life. There would be a lot of tags.
If I organise things by a tag hierarchy, I can't search all the notes in a top level tag easily, as I can with notebooks. If I click a top level tag, it returns all the notes below it, but if you then search, it searches all notes.
Finally, it's really easy using drag and drop to organise my notes with notebooks. But with tags, it's quite a bit harder. To move notes between tags, you have to type the tag and delete the old one. That's two steps, instead of dragging and dropping. And I also have to remember what tag it should go under (I can't use drag and drop to find where it's going), and not do a typo (it's easy to do) and file it somewhere else.
If you can show ways around these frustrations, I'd be grateful.
This is a consequence of wanting notes to only be in one location. Tags are not conducive to that end. I agree they are an organisational structure (my bad), but you've sharpened what I was trying to say:
Most notes (like most things in the universe with a name of any kind) have only one primary defining feature: Work notes are first and foremost about work, not anything else. Tags, by their nature, do not easily recognise a primary feature, although they pick up non-primary features easily and can accommodate the messiness of non-primary hierarchies. Notebooks do recognise the primary defining feature of each note. The primary feature of a note is nested, however. It has a single chain of hierarchy associated with its primariness (that's what you used to classify it as primary). If you had more than one chain, the feature wouldn't be primary, it would be ambiguous (is it classified as this or that or both?). The primary nature of a note is excellent for organisation, because it is where it is most dissimilar from everything else. Let me know if you find my reasoning faulty.
Notebooks are like taxonomy: a species can only be classified one way. Tags are like attributes: a species can have several colours. Especially in creative work, it's very helpful to do the latter. The seven major classifications of taxonomy (Kingdom, Phylum, Class, Order, Family, Genus, Species) are enough to adequately classify all of life on earth. My question is whether the three levels in Evernote are adequate to classify everybody's notes in Evernote. To capture most of the major sources of variation in human life with the fewest possible categories, I think you need four levels (Areas of responsiblity>Roles/Projects>Role/Project parts>Information block); I don't think three is enough. If I only had work in evernote, I'd be fine - I'd have cut out one level. But I don't - I have work, family, hobbies etc.
I suspect Evernote has run trials with different types of hierarchies, and three came out best, so I'm probably wasting my time here. But if they haven't, that's what they should do.