Sunday deliveries will be expensive for the USPS to accomplish, so this cost will be passed on to Amazon.

Now the bottom line is will this add to Amazon's bottom line? What percentage of their costs will be Sunday deliveries? Will customers be attracted to Amazon by more than low prices but by the fact that they could receive their purchase one day sooner?

Will Amazon make up the additional cost to them by adding a few cents to each package they ship, or will the cost of two day shipping increase to everyone just so those living in the test markets can receive their packages sooner?

If there is not a profit to Amazon in this venture I doubt it would be going forth. As far as the USPS picking up additional business goes I do not see the harm in this. UPS or FedEx are under no restraints that would prevent them from offering the same service.