I think the concept that the author started with is fascinating: that humans could be genetically modified to not require sleep. One of the effects of not needing sleep is that they are more productive, can spend more time working and learning, and become therefore somewhat super-human. This leads to a great deal of resentment and even hatred from "Sleepers", and the story evolves from there. One of the difficulties I had with this book is that I had a hard time relating thoroughly to any of the characters. Leisha Camden is the most prominent and sympathetic character throughout most of the book, but still not fully understandable or easy to empathize with for some reason. When the story took us to the orbital, I found Miri to be a much more interesting character and really enjoyed that part of the story. All in all, an engaging story that left me with lots to think about.
One thing I kept thinking about while reading this book is what it would feel like to not sleep. I LOVE sleeping, and hitting the snooze button and sleeping some more. I almost felt sorry for the Sleepless folks; while sleep is a necessity for us, it is also a hedonistic joy :)