Of the people I follow, who do they follow that I don't follow? (sorted by count of people I follow)

who_should_i_follow.rb

require 'rubygems'
require 'json'

user = ARGV[0]
if user == nil
  puts "usage: who-should-i-follow.rb screen_name"
  exit 1
end
followers_to_check = 100

def get_followers(screen_name)
  JSON.parse `curl -s http://api.twitter.com/1/friends/ids.json?screen_name=#{screen_name}`
end

def followers_of(id)
  JSON.parse `curl -s http://api.twitter.com/1/friends/ids.json?user_id=#{id}`
end

def get_user_names(ids)
  JSON.parse  `curl -s http://api.twitter.com/1/users/lookup.json?user_id=#{ids.join(",")}`
end

f = get_followers(user)
followers_of_followers = f['ids'].first(followers_to_check).map do |id|
  followers_of(id)['ids']
end

followers_of_followers.flatten!

followers_i_dont_follow = followers_of_followers - f['ids']
sorted = followers_i_dont_follow.group_by {|i| i}.sort{|a,b| b[1].size <=> a[1].size}

hash_ids = {}
sorted[1..10].each {|i| hash_ids[i[0]] = i[1]}

user_names = get_user_names(hash_ids.keys).map {|user| [user['screen_name'],user['id']]}

puts "You should follow (since x of your users follow):"
user_names.each do |name|
  puts "#{name[0]} (#{hash_ids[name[1]].size})"
end

Gave a shout out to this gist here: http://blog.jerodsanto.net/2009/05/expand-your-twitter-network-in-less-than-15-lines-of-ruby/