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.
USPS First-Class Mail<sup>®</sup> Parcel
This download contains the nopCommerce recommended 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)