rails-upgrade is now an official plugin

To use it now, simply install the plugin:

script/plugin install git://github.com/rails/rails_upgrade.git

The plugin adds the following tasks:

rake rails:upgrade:check      # Runs a battery of checks on your Rails 2.x app
                            # and generates a report on required upgrades for
                              # Rails 3
rake rails:upgrade:gems       # Generates a Gemfile for your Rails 3 app out
                              # of your config.gem directives
rake rails:upgrade:routes     # Create a new, upgraded route file from your
                              # current routes.rb

http://omgbloglol.com/post/364624593/rails-upgrade-is-now-an-official-plugin