console

u = User.new
u.images
NoMethodError: undefined method `images' for #<User:0x3666c98>
	from /usr/local/lib/ruby/gems/1.8/gems/mongo_mapper-0.7.6/lib/mongo_mapper/plugins/dirty.rb:25:in `method_missing'
	from (irb):9


u.user_images
=> []

user.rb

class User
  include MongoMapper::Document
  many :user_images, :as => :images
end

user_image.rb

class UserImage
  include MongoMapper::EmbeddedDocument
  
  key :source_file_name, String
end

For anyone who comes across this, the line:

many :user_images, :as => :images

should be:

many :images, :class_name => "UserImage"