I have been having this problem as well. I rarely use USPS anymore, this is only one of a myriad of reasons. If you are going to be shipping a lot, I highly recommend looking into FedEx discounts. With any sort of volume, the ground shipping in good seasons is cheaper than priority and 1-2 days.
USPS will accept PayPal for payment now. I used that option when someone sent me postage for an RAOK as a gift, rather than for services. I noticed PayPal having some issues too, but it hasn't slowed me down.
I use USPS several times a day through eBay/PayPal shipping. I haven't seen that message in months. Now the fact that their service doesn't support a label printer on apple is a real pain. I have to create a PDF and print that. lol
Seems to happen a lot. I have to use fedex from work, but anything from home i use USPS or UPS.
I'm a bit anti fedex since they got busted a few months ago screwing everyone by overcharging everyone for years :P http://www.bloomberg.com/news/2012-1...mail-says.html