A lire ce post de 37signals.com sur les formulaires d'inscription qui en vient à cette démonstration : don’t ask for it if you really don’t need it. If a field is optional consider leaving it off the page during the add process. Display it on edit, but hide it on add.

http://37signals.com/svn/archives2/push_optional_data_entry_as_far_back_as_you_can.php