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.
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