Would be great with support for (embedded) value objects in Mongoid. Examples of common value objects would be temperature (degrees + scale), money (amount, currency), address (street, city, country), etc.

The major difference would be that value objects don't have any ids. Comparison and a few other aspects are also different.

Reference:
http://api.rubyonrails.org/classes/ActiveRecord/Aggregations/ClassMethods.html#method-i-composed_of
http://martinfowler.com/eaaCatalog/valueObject.html