Allowing users to add taxonomy terms but requiring administrators to verify them
Brainstorming here...now that taxonomy is part of the entity system, it should be possible to do something like this:


Install http://drupal.org/project/workflow
Add a field to your taxonomy called "Published" or "Approved" that is a boolean checkbox
Setup a workflow that is triggered on taxonomy term creation with Approved as a field only accessible to admins
Write a hook into taxonomy terms that removes a term unless it is approved (this is the tricky part - there are a lot of ways to get to taxonomy terms, so this might make this approach moot).


Alternative:
Since you mentioned a user filling out a form - you could pretty easily have a content type called "Taxonomy Term" or something with the needed Taxonomy fields, then use workflow/Rules to send the submission to an admin, upon approval use Rules or custom code to create a new taxonomy term.