For the past three years, Phillip Herr of the US Government Accountability Office was tasked by Congress to find out what's wrong with the US Postal Service.
He came to this conclusion (unsurprising to some, I'm sure):
Herr and his team concluded that the postal service's business model was so badly broken that collapse was imminent. Abandoning a long tradition of overdue reports, they felt they had to deliver theirs 18 months early in April 2010 to the various House and Senate committees and subcommittees that watch over the USPS. A year later, the situation is even grimmer. With the rise of e-mail and the decline of letters, mail volume is falling at a staggering rate, and the postal service's survival plan isn't reassuring. Elsewhere in the world, postal services are grappling with the same dilemma—only most of them, in humbling contrast, are thriving. [...]
The problems of the USPS are just as big. It relies on first-class mail to fund most of its operations, but first-class mail volume is steadily declining—in 2005 it fell below junk mail for the first time. This was a significant milestone. The USPS needs three pieces of junk mail to replace the profit of a vanished stamp-bearing letter.