After some truly horrific experiences with the post office in recent weeks I am switching to UPS when I send my books to LBC. Should the box be large, that is. Small shipments, say four binds or less, I'll stick in a flat rate box.

By the way, I still have many original flat rate boxes, which are larger than the current ones. 10% to 20% extra on all four sides = way easier to ship with bubble wrap for proper protection.