I'm using the method given at http://drupal.org/node/357328#comment-3021230 to disable a submit button in a form (after trying to simply set #disabled in hook_form_alter). I have the module set with a weight of 10, the code works as it should in terms of setting the attribute for the field (below), but the field is not disabled. I note that the attribute is being set to 'disabled' rather than TRUE in this and another almost identical example. I tried it with TRUE just in case, to no avail.