Courage!

unfollow.rb

require "rubygems"
require "twitter"

# get these from apps.twitter.com
CONSUMER_KEY = "abcd"
CONSUMER_SECRET = "abcd"
OAUTH_TOKEN = "abcd"
OAUTH_TOKEN_SECRET = "abcd"

TWITTER_USER = "your_username" # needs to be the one associated with keys above
TIMEOUT = 5 # a good default value

client = Twitter::REST::Client.new do |config|
  config.consumer_key        = CONSUMER_KEY
  config.consumer_secret     = CONSUMER_SECRET
  config.access_token        = OAUTH_TOKEN
  config.access_token_secret = OAUTH_TOKEN_SECRET
end

the_preserved = ["usernames", "you_do_not", "want_to_unfollow", "here"]
the_preserved = the_preserved.map do |username| username.downcase end

puts "Preserving:"
puts the_preserved
puts ""

following_ids = client.friend_ids(TWITTER_USER).to_a
save_file = File.open("followings-bkup.txt", "a") # open in append mode

following_ids.each do |id|
  name = client.user(id).screen_name.downcase
  if the_preserved.include?(name)
    puts "...preserving #{name}"
  else
    begin
      puts "UNFOLLOWING #{name}"
      client.unfollow(id)
      save_file.puts name
      save_file.flush
    rescue Twitter::Error::TooManyRequests => error
      puts "Got an error, probably rate-limiting... waiting to try again"
      sleep(error.rate_limit.reset_in)
    end
  end
  sleep(TIMEOUT)
end

puts "done!"