Change -Year label in Views Exposed Filter to <Any>

Found a way to do it. You can edit date_api_elements.inc line 219 and add :
$element['year']['#options'][''] = 'your string';

Could be nice to have a variable_get instead of 'your string' to define it somewhere.

Hope that helps

Here is a quick patch to fix this.

@julien, how to do this in version 7.x-2.7

Looking at this new version code, maybe you can try to use this theme function in template.php of your theme, see if it works. Haven't tested so i'm not too sure. Check if you can alter the element variable maybe.

/**
 * Returns HTML for a date select input form element.
 */
function theme_date_select_element($variables) {
  $element = $variables['element'];
  $parents = $element['#parents'];
  $part = array_pop($parents);
  return '<div class="date-' . $part . '">' . theme('select', $element) . '</div>';
}

So I was looking into this myself for 7.x 2.x-dev and found this.

Look into module/date/date_api/theme/theme.inc and you'll find starting at line 104 the functions that generates the starting date label. Such as

function theme_date_part_label_year($variables) {
  return t('Year', array(), array('context' => 'datetime'));
}

So basically I copied that function into my template.php as so:

function templateName_date_part_label_year($variables) {
  return t('All', array(), array('context' => 'datetime'));
}

And it works great.

@jerrylow, thanks for that, indeed it's better using this than my solution.