Cannot alter title on user profile page
Yeah, that's an odd approach with === isset() basically checking if drupal_get_title == TRUE; whereas drupal_get_title returns a string title.

Something like this should work, in template.php or module (clear cache).

It will set the $title variable for page.tpl.php

/**
 * Implements hook_preprocess_page
 */
function MODULE_preprocess_page(&amp;$variables){
  // Set title on user account pages.
  if ($account = menu_get_object('user')) {
    $variables['title'] = t('My Sharecab');
  }
}