In some ways, I understand not adding a folder structure because tags can do the same thing and allow docs to be in two folders at the same time by using 2 tags, but it lacks visualization and humans are very good at looking at structures and pulling out meaning and understanding.
Evernote should consider the use of a few visualization concepts
Tag Graph - Would visualize every tag into a graph structure which would allow users to navigate and even edit through drag and drop of tags and even notes that have tags applied.
Apply a combination of statistical AI and Symbolic AI to yield graphs that would infer connections between notes and suggest tags (This is kind of similar to "similar notes" feature).
