I have never seen pork graded for the consumer, but I believe it is graded for commercial buyers (packers, butchers). I read somewhere that most pork in the US is graded "US1," but there's a 2 through 4 also. I'm sure that means something to the packers, but is not passed on to the consumer. I know it has to do with the amount of fat on the back strap.
What matters more, with pork, is where you buy it. WalMart tumbles their pork products (means it's infused with a salt solution), so you're paying for 10-13% salt water. Sam's Club, on the other hand, doesn't add anything to their pork. I've used both, and greatly prefer the pork I get without solution added. I try to look for the cuts that are a little more pink, and are firm.