Formulists is something I wish I had thought of.
“Formulists is a list creation and management tool that allows users to effortlessly generate dynamic and personalized Twitter lists that continuously self-update.” You select from a menu of pre-sorted filters that you edit and customize to meet your needs. The resulting Twitter lists generated by the service are then updated from daily to every few days. I’m looking forward to using my newly created “people I recently followed” list.
I’m a huge fan of intelligent listening tools. If this works as advertised, it definitely falls into the smart category. Here’s a screencast to show you how it works.