So if you have ordered something before signing up for Prime that will come out later (for instance, the forthcoming George R. R. Martin novel) you will wish to now cancel that order and re-order it, so that you can avoid the shipping charges, as that's what you pay the $70/yr to Amazon for. Re-defining the shipping speed doesn't change the shipping costs down to nil. Which blows.
What the hell is that shit?
Anyways, just reordered Feast for Crows and the new Harry Potter book for about $30 less than I was going to pay, as with Prime, 2-day shipping is free.