Consider:

1.9.2-p290 :001 > MyModel.first.clone.created_at
 => 2012-06-06 13:46:25 -0500
1.9.2-p290 :002 > MyModel.new.created_at
 => nil

If the model includes Mongoid::Timestamps, clone() should set created_at and updated_at to nil, so it is set when the object is persisted