cryptic "Routing Error" when ApplicationController has a bug

In a brand new, empty rails 3.0.0.beta app that has the following application controller:

class ApplicationController < ActionController::Base
  include ModuleThatDoesntExist
  protect_from_forgery
end

With the following concrete controller:

class FooController < ApplicationController
  def index
    render :text => "Bar"
  end
end

... and these routes:

Rails3test::Application.routes.draw do |map|
  root :to => "foo#index"
end

Accessing the root URL returns a "Routing Error: No route matches '/'" message instead of a more helpful error about ModuleThatDoesntExist not being found. This can make debugging the upgrade to rails3 tricky, suggesting developers look in the wrong place for the underlying issue.