Difference between Rails 2.3 and 3

(1) Introduction of bundler (New way to manage your gem dependencies) 
(2) Gemfile and Gemfile.lock (Where all your gem dependencies lies, instead of environment.rb) 
(3) A new .rb file in config/ folder, named as application.rb
 (Which has everything that previously environment.rb had) 
(4) Change in SQL Structure: Model.where(:activated => true) 
(5) All the mailer script will now be in app/mailers folder, 
earlier we kept inside app/models. 
(6) Rails3-UJS support. for links and forms to work as AJAX, 
instead of writing complex lines of code, we write :remote => true 
(7) HTML 5 support. 
(8) Changes in the model based validation syntax: validates :name, :presence => true 
(9) Ability to install windows/ruby/jruby/development/production specific gems to Gemfile. 
group :production do 
 gem 'will_paginate' 
end