I ship 10-20 packages a day via Priority Mail for asmall web based business that I own and I can count on 1 finger the number of delivery problems I've had in the last 2 years. Was never a fan of the USPS in the past but I am now.
I cannot count on the mail being delivered at any set time. We get mail personnel who speak no english as well, I don't know how they can do the job.
That's because FedEx provides their linehaul now.