I didn't know this book existed until I heard the author, Nancy Kress, reading it at a WorldCon panel. She read the first five or six chapters, and I bought and downloaded the book to my phone before the reading was over.
At 38,000 words, it's a novella, the author's favorite format. The short length was also nice because I was able to finish the book in one day between panels. Ms. Kress said she likes the format because it's nice to be able to tell a whole story without needing all the underlying threads. (I like both formats, as a reader.) The book was great.
Earlier at WorldCon (2012 in Chicago), the author was on a panel called Moral Ambiguity. She didn't give anything of her story away in the panel, but she did make it so I thought about the book a bit differently than I might have if I hadn't attended the panel. 
Is there a way you can think of to sympathize with baby and toddler kidnappers? Can it ever be acceptable for a near-menopausal woman to get knocked  up by a fifteen-year old?  Can one bacteria make a simple mutation that messes up everything?
As is characteristic of Kress stories, it features a lot of moral ambiguity, multi-dimensional characters, and "fun" science extrapolations.
I give this a four of five. I might nominate it for next year's awards, and I'm going to stick it in my husband's reading queue.