Penny, you hit on what is generally wrong with Nova the last decade, but I had a different take on this one: I thought it came down very heavily in favor of the impact...like the ice layer diamonds had proved it (I'd like to see more systematic sampling, and it was not clear how well the layer they found diamonds in was dated (by comparing oxygen isotopes to the global curves, I suppose)). But, I thought it was kind of neat how they were able to identify ice age ice from warmer time ice from colder Younger Dryas ice (by color/dust).
Chris