I've recieved this email about USPS updates
Web Tools Customer,
USPS will release updates to the Web Tools APIs on 28 July 2013. The staging environment is currently open for testing your updated applications. You may review staging information and the release notes at the USPS Web Tools site here https://www.usps.com/business/web-tools-apis/welcome.htm for more details.
If you rely upon a third-party developer (e.g. software or ecommerce/cart provider) for USPS products and services on your website or your shipping application, please direct any application-specific questions to them.
For questions and concerns, please contact our customer support at 1-800-344-7779 or [email protected]
Web Tools Program Office
You can read about the changes to the rate response values
(see appendix A)
These look to be breaking changes. In more friendly language, you can read about their Making Priority Mail Better
To simplify the product names, Express Mail will be called Priority Mail Express™. It remains our fastest product available, offering the same great service as Express Mail just with a new name. Express Mail International® will be renamed Priority Mail Express International™.
That name change will likely break the USPS plugin.