there's a massive difference between tagging-for-self-recall and tagging-for-other-recall. when i invented tagging the first was paramount, but the latter has become dominant and has very different design considerations

one interesting note: you can infer a bunch of hierarchical information since people frequently tag from broader to more specific, topicwise.

some things can be tagged by multiple people and you can thus infer synonyms as well. this can thus be fixed in search.