Taxonomy

This would be quite useful functionality, and i'm sure i've seen it implemented or at least requested somewhere.

In effect, it makes the hierarchy in a vocabulary just an organizing tool, preventing the grouping labels higher in the hierarchy from being used as terms.

By clicking the wrong Add terms link, i managed to add a couple terms to the wrong vocabulary.

One of the powerful things about taxonomy is that all terms are really equals under the hood, no matter what vocabulary they belong to. Unfortunately, Drupal does not make this power available through the UI. We can, however,

Checkboxes are more user-friendly than multiple-select option form field.

Taxonomy Super Select seems to be the popular choice.

Better Select worked better for our needs, however:
http://drupal.org/project/betterselect

Fortunately, it has a node form only option. It also has an always save parent also option! All under Administer » Site Configuration » Better Select.

Note that Content Taxonomy would also be an option for this functionality.

I can't believe no one has done this!

Simplify the taxonomy interface for administrators by removing the taxonomy related terms box...

drupal taxonomy hide related terms
drupal form tweaks remove related terms

The commit message upon completion...

"Clean taxonomy term add / edit form by removing related terms and moving parents from the closed advanced fieldset to the open identification fieldset if the vocabulary has already been made hierarchical."

And the code: