twitter_avatar_to_address_book.rb

#
# Assuming your address book entries have a URL field 'twitter' containing either their full Twitter URL, or just  
# their username, go fetch the image and drop it into the addressbook.
#
# Works for me, but your milage may vary.
#

require 'rubygems'
require 'twitter'
require 'open-uri'
require 'fileutils'
require 'appscript'

include Appscript

httpauth = Twitter::HTTPAuth.new('USERNAME', 'PASSWORD')
client = Twitter::Base.new(httpauth)

address_book_image_dir = File.expand_path("~/Library/Application Support/AddressBook/Images/")

app("Address Book").people.get.each do |person|
  person.urls.get.each do |url|
    if 'twitter' == (url.label.get.downcase)
      puts "Updating avatar for #{person.name.get}"
      twitter_url = url.value.get
      twitter_id = twitter_url.split("/").last      
      friend = client.user(twitter_id)
      twitter_avatar = friend.profile_image_url.gsub(/_normal(\.[a-zA-Z]+)$/, '_bigger\1')
      new_image = File.join(address_book_image_dir, person.id_.get.split(':')[0])
      File.open(new_image, 'w+') { |f| f.write open(twitter_avatar).read }
    end
  end  
end