I just completely overhauled my Twitter lists, a few days after impulsively unfollowing everyone who didn’t follow me back. I deleted many lists and added many users to the ones I kept. I used Twitter List Copy to import all the users on other people’s lists into pre-existing lists of my own.

It uses oAuth so it’s password-free, and despite the disclaimer on the site, it seems to merge imported users with your pre-existing lists just fine. Thanks to Noah Liebman, who built this awesome tool. Follow him on Twitter or check out his website.