During the Check-out process, Payment Information
Why is it so that the user has to enter the Purchase Order Number
since it is automatically generated after that the Order has been placed.
in the one-page checkout, would not it be nice if instead of a text box, there would have been a label with the generated purchase order no and a sign indicating:
This is your generated PO number, please keep it safe for reference (or when the delivery guys will be knocking at the door, they will confirm the PO order with this generated number)