USPS made some changes that have caused a few issues. We're starting this thread to unify a few others.
The changes USPS made had two direct issues:
1) The rates had a bunch of "garbage" as USPS started adding the (R) and (TM) symbols to the rates returned. This didn't prevent checkout but did look ugly.
2) USPS First Class Mail wasn't showing up for domestic shipping options.
We fixed the garbage earlier today, and soon after fixed the issue with First Class Mail, but in doing so discovered another issue where additional first class rates were being returned. We have a fix for that and will be pushing it to our production environment as soon as it's fully tested, which we anticipate being in the next 12 hours or sooner. We'll update this post and this thread as it happens.