I will try to break down what I needed to do to get usable USPS shipping quotes.
Step 1) make sure you have a recent version of Ãœbercart and the uc_usps module, I would recommend at least alpha7b with the patch I have posted here:
http://www.ubercart.org/forum/development/1452/uc_usps_module_patch_and_...
or the latest development version from the Ãœbercart bazaar repository. And that you have enabled the "shipping quotes" and "US Postal Service" modules. And that your user has permissions to "configure quotes" for the "uc_quotes module".
Step 2) create or login to your USPS.com account and sign up for a Web Tools User ID. Its not real easy to find where to sign up for access to the Web Tools, it is in a box on the right hand side of the page at http://www.usps.com/webtools/ entitled "Access USPS Web Tools".
Step 3) Once you have received your email with your Web Tools User ID in it, contact USPS personally and request access to the production server by email (icustomercare@usps.com) or phone (1-800-344-7779) because the requests Ãœbercart sends out will not work at all in testing or production mode if USPS does not grant you access personally. You may need to tell them that you have successfully completed testing of your shipping quote solution.
Step 4) enter the "Web Tools User ID" you received in the email from USPS.com into Ãœbercart's "USPS User ID" on the /admin/store/settings/quotes/methods/usps page. The "USPS password" is not used and not needed. And select "production" mode, as nothing will work in 'testing' mode.
Step 5) Setup the weight in pounds and/or ounces for all of your products in thier product settings.
Step 6) Fill out your default store address in the shipping quote settings, as usps will need the zip code from those settings.
Step 7) Attempt to get a shipping quote by adding things to your cart and checking out, fill out the forms and be sure to enter a shipping zip code.
At this point it should work, and you should get usable shipping quotes in the pane during checkout, if not, and the user you are logged in as has access to "configure quotes" for the uc_quote module you should see the XML response that USPS.com Web tools returned from Ãœbercart's request in the shipping quotes checkout pane, which is very useful in determining what might have gone wrong.
I hope this helps some people out and please feel free to let me know if anything here is not clear, or just plain wrong.