I would like to be able to use a widget along the lines of active tags autocomplete that would allow me to maintain a taxonomy hierarchy. I need to be able to select multiple terms, including multiple children for one parent. Any recommendations?
There is a module for that. Probably the only way to select multiple is to allow the field to have multiple values. http://drupal.org/project/term_ref_autocomplete
Use autocomplete deluxe module https://www.drupal.org/project/autocomplete_deluxe thi replaces the normal autocomplete box with another textbox with auto complete with ability to add more terms (like when entering multiple emails in the email)