I located a full PDF on the new rates at USPS.
http://www.usps.com/rates/welcome.htmAnything shipped from the 12th forward would use the new rates.
Agree on those Priorty prices AND they have a new LARGE FLAT-RATE BOX for $12.95. If you have an account at USPS (no charge), you can get free delivery on any of the free Priorty boxes, including the small and medium video cassette size boxes (I use them alot and just got more).
ebay sent out a message on April 22nd on the new rates. Their tables should be working by now, but I don't have anything listed currently. I haven't seen Auctiva post a notice, but I would bet they are ready (and it may just be a feed from ebay anyway).
I would do the old double-check the invoices for the first few weeks to make sure they are correct for calculated. You can also cross-check with their shipping calculator:
http://payments.ebay.com/ws/eBayISAPI.dll?EmitSellerShippingCalculatorDanno