I was trying to override the title for the review page of the cart (cart/review), which is originally "Please review and submit your order", using the menu.module, and noticed it wasn't working. Digging in the code, I found a call to drupal_set_title in checkout_review_form() function, which prevents menu.module from overriding the menu title. Removing the call to drupal_set_title in checkout_review_form fixes the problem.