I have been an Amazon Prime customer for years, and have been very satisfied to get the free two-day shipping. And they have always done a good job with this, and in the past I have had literally hundreds of shipments in a row arrive on time.
However, two of my last three orders have been late, and the last order, which should have been here on Thursday, still, two days later, has not arrived despite the fact the system says it was delivered June 23 at 12:54.
But it is actually fairly easy to figure out why the service has deteriorated. On both these late orders, Amazon used the USPS to deliver the package. That explains a lot. The USPS has awful, unreliable service and has absolutely no package tracking capability. Not only is it my package missing, but neither Amazon, myself, or the USPS have any way to find out where it is.
This is awful service. I am not only a pretty high-volume customer, but I have paid an annual fee to get premium shipping -- and I can tell you that there is likely no one on Earth who considers the USPS a premium shipping option. If they keep sending my 2-day packages snail mail, there will no longer be any point to being a prime member. Maybe they will offer a super-prime membership sometime in the future that guarantees they will not use USPS (though I suppose I can get this now by clicking the one-day shipping button and paying the $3 or whatever it is extra).