When the USPS updated their Web API on July 28, 2013, it caused the nopCommerce USPS plugin to dispaly jibberish for the available shipping methods.
This download contains the nopCommerce recomended fix for this issue. See the post on nopCommerce here.
See help on NopCommerce for installing a plugin here. (though all of these steps are not required if you are replacing the USPS plugin)