Rails 3 associations eager load of associated classes significantly slows down development environment

In rails238 the associated classes were not loaded until an association method was called. I'm sure this was a performance improvement in production, but with a class like User that is associated with about 50 other models which have their own nested associations, this significantly slows down requests, since User is reloaded on every request. I'm wondering if we could create development environment only behavior to lazy load scopes and associations. My User model takes about 7seconds to load.

Here's how I repro'd the issue in both environments:

I created the following two models:

#user.rb
class User < ActiveRecord::Base
  has_many :documents
end

#document.rb
raise "I'm loading"
class Document < ActiveRecord::Base
end

I opened up a console:

> User
RuntimeError: I'm loading ###in rails3 but not rails238







> User.new.documents
RuntimeError: I'm loading ###in rails 238