I find it interesting that people against single-payer always reference the USPS as an example of government inefficiency. In reality, the USPS, while admittedly not the picture of efficiency by any means, is actually an example of a government program that DOES work!
Each year, the USPS actually makes a profit, 200 million dollars for first quarter of 2012 for example. (
http://www.nalc.org/PostalFacts/02102012_statement.html)
The reason why the USPS has been in the red for the past few years actually has nothing to do with the efficiency or profitability of the post office. It is because a 2006 mandate forces the post office to PRE-PAY the health care benefits not only of current employees, but also of all employees who'll retire during the next 75 years. This mandate costs 5.5 billion dollars a year, and is in effect through 2016.
I'll also add that the USPS makes an operational profit despite the fact that it is legally bound by a universal service obligation to provide its services to the entire nation, no matter how remote they are, and at an affordable price. Corporations like FedEx or UPS can cherry-pick which locations to offer services to, and they are only involved in the delivery of packages, the most profitable service.
More info:
http://www.pbs.org/wnet/need-to-know/five-things/the-u-s-postal-service/11433/
http://about.usps.com/universal-postal-service/usps-uso-report.pdf
Anyway, as far as single-payer goes, every other developed country except for the US has a single-payer system or some form of government run universal healthcare system, and guess what? They are all more successful than the US system, both in terms of healthcare outcomes and in financial spending.
You can argue that infant mortality or life expectancy aren't good indicators of health outcomes, but I'd challenge you to find a better metric which really covers the ENTIRE population, not just those that can afford treatment. They're not perfect indicators, but they are what is universally used and accepted. I'll agree that the US system does have the best care for people with money to spend, but for those that don't it's abysmal.