Got myself a copy last night. I was very happy with it and left comments to that effect on RPGnow. Here are some other things I didn't put there.
I was really surprised (pleasantly) by what wasn't there. No PrCs. No spells. There are a ton of these as it is. A couple of each would have been nice, but it's not like I'll miss them.
I also thought the weapons section was a little light. Really though, in a stone-age setting, once you get past pointy-stick vs. blunt-stick, there probably isn't a lot left to do. (If you haven't got the book, there is more than this here. I'm just oversimplifying.)
Overall, I was very pleased with my purchase. Do you have any similar products in the works? More "setting starters" I guess?