Drupal override search form: how to debug hook failure? In the past I've always been able to override the theme form using the method mentioned http://drupal.org/node/154137. 

function YOURTHEME_form_alter(&amp;$form, &amp;$form_state, $form_id) {
    if ($form_id == 'search_block_form') {
        $form['search_block_form']['#title'] = t('Search');
    }
}


However, this doesn't appear to be recognised in the template.php of my latest theme. It hasn't been an issue in the past - what is the best way to debug why the hook doesn't appear to be activated?
Clear cache.
Place some debugging code to see if the hook and then if statement is called.
Inspect the form variable, does it look correct?