I actually picked up this book on a whim, so i was twice as amazed at this book. I often enjoy books that push the boundrys, and as you put it,'GNP', it dose just that.
I even put in the time to go to Elizabeth Bear's homepage and read in interest about this book and any of her other works. to answer you'r question, or at least part of it, she said that they came up with the idea(s) emailing each other. That it was origunally intended to be short but grew out. (not her exact wording) I hope that helps. I just really liked this book, so i thought i'd help answer a fellow fans interests.