Could the NSA Keep Track of Who You Send Letters To?

OK, this is just out of curiosity. Suppose the government started up a program that tracked everyone’s mail. They didn’t open letters to read them, they merely kept track of the address, return address, and postmark date for every piece of first class mail and every package that anyone sent anywhere. This metadata would, naturally, be collected for anything sent through the postal service, but also for packages sent via FedEx, UPS, and so forth. The postal system is pretty automated these days, so this probably wouldn’t be all that hard to implement.

Anyway, how do you think the public would react? Would people care more about this than they do about phone and email records? What do you think?