I have for a while wondered about an ideal (good) approach to storing api keys in config files in ruby projects. A few conditions must be met:
1) A new user must be given clear instructions on what has to be configured (until it is done), with boiler plate to complete.
2) git must not accidentally let you submit the key.

Gregory Brown steered me towards this setup. Create a config.rb file fill out the template for adding data. Then copy it to config.rb.example and add config.rb to the .gitignore

touch config.rb
#setup template of config.rb
cp config.rb config.rb.example
echo "config.rb" >> .gitignore
git add config.rb.example

The file requiring the keys can then do something like:

begin
  require "config"
rescue LoadError
  STDERR.puts "You need to create a file called config.rb. See config.rb.example"
exit

A slightly larger example.
shorturl.rb

  require 'net/http'
  require 'rubygems'
  require 'json'
  require 'cgi'

  begin 
     require File.dirname(__FILE__) + '/bit_ly_key'
  rescue LoadError
   STDERR.puts "You need to create a file called bit_ly_key.rb. See bit_ly_key.rb.example"
   exit
  end

  module TechNews
     class Shorturl
        def initialize( url=nil )
           bit_ly_keys = TechNews::BitLyKey.new

           ##  url encode
           url ||= "http://amaras-tech.co.uk"
           @long_url = CGI.escape( url )
           payload   = "http://api.bit.ly/v3/shorten?login=#{bit_ly_keys.login}&apiKey=#{bit_ly_keys.apiKey}&longUrl=#{@long_url}&format=json"
           @response = Net::HTTP.get URI.parse(payload)
           @response = JSON.parse( @response )
        end

        def get_shorturl
           return @response["data"]["url"]
        end

     end
  end

  if $0 == __FILE__
     x = TechNews::Shorturl.new()
     puts x.get_shorturl
  end

bit_ly_key.rb

# Register at [1] and get api key [2]
# [1]: http://bit.ly
# [2]: http://bit.ly/a/your_api_key

module TechNews
   class BitLyKey
      attr_reader :login, :apiKey

      def initialize
         @login  = ""
         @apiKey = ""
      end

   end
end