I've just finished reading this. It's amazing, seriously amazing. My favourite part is probably Sloosha's Crossin', which is so believable and eerily beautiful. The Sonmi section and the Frobisher letters are incredible too. It's wonderful how the same sort of themes echo through all the stories and it's basically saying that human nature is always irrevocably the same. On the way back through time (if you see what I mean) it's quite creepy as you start to notice how each story points to the end.
I'm pretty sure this was a DiSer's recommendation, so thanks.