The tool allows you a few options – Unfollow all who do not follow you back, Unfollow all, and Follow all who follow you. You can also add in up to 50 users who won’t be affected by the action, so if you have a particular celebrity that you like to track or thought-leader who doesn’t subaction showcomments propecia optional blog follow you but you want to keep tracking, you can exclude them from the action.
This service is free for accounts with up to 1800 followers or friends. For larger accounts, this can be used up to three times for free.
This isn’t a recommendation to use this tool – I don’t think that either bulk following or bulk unfollowing is a great Twitter strategy. But I have heard from many people who are looking for a tool to accomplish this exact functionality, and have seen Huitter’s tool work effectively.