In keeping with modern conventions, I would love to see an option for multi-value fields alongside popup menu, drop-down value list, checkboxes and radio buttons.
This option would be called something like "Tag" and would:
1. display field values in their own bubbles with a delete "x" button to one side
2. type-ahead much like drop-down lists currently do to auto-fill existing tags
3. be styled using their own CSS styles.