When creating successive notes in Evernote that have the same tag ("Birthday Plans" for example) and importing them as Drupal nodes, each new node creates a new instance of the taxonomy term. So, after 10 notes tagged "Birthday Plans" the taxonomy contains 10 instances of the term "Birthday Plans." When viewing the taxonomy for any of them (i.e. taxonomy/term/) you see only the nodes for that instance (i.e. one node), thus effectively defeating the purpose of taxonomies/tags in the first place and filling the taxonomy with identical terms.