USPS shipping module trouble

suddenly today. It was working and still sometimes does, sometimes after refreshing the page a time or ten, it works, but my client says her customers are seeing this alot (and I did, too, when I did a couple of tests):

We are unable to find a USPS shipping quote suitable for your mailing address

Could this just be a problem with server load at USPS? Nothing has changed on the client's end.

As you'll see in hundreds of other posts in the last couple days, USPS is having problems with their servers since Dec 8.

You are advised to set up some other shipping quote options such as table-rate or flat-rate until they sort out their issues.

Thanks, DrByte! I had a feeling that was the problem, but I didn't want to tell a client that without hearing it from someone here to back up my theory. I appreciate the quick response.

Oh, and I searched here first to try to find someone else having the same problem and didn't find any posts...how did I miss them?