For ad hoc Rails tasks we have a few implementation alternatives, chief among which would seem to be:
script/runner some_useful_thing
In Rails 3.0+, the config/environment.rb requires the config/application.rb, that requires the config/boot.rb.
config/environment.rb
config/application.rb
config/boot.rb
So, to load an app in Rails 3, you still only have to require the environment.rb
environment.rb