What is the best method to build a form to track N number of values? I have to create a block that will be a gallery of users. The users to be featured will be curated by site editors. So I'm thinking the best way to track this is a pretty simple Drupal form / settings page where they just enter in the usernames they want.

However, the form should track N number of users. Is there a way in the Forms API to have an element that includes an "Add another value" or something similar, to allow for unlimited entries?

Or would it be better to just have a text area and ask the user to fill out one username per line?
That, or step 1) you could use http://www.drupal.org/project/flag which would allow the editor(s) to click / unclick a toggle on a user's profile that says they are "curated" and step 2) create a view that lists which users have been flagged.