Fark linked up this Wired article detailing a new theory about the extinction of the dinosaurs. By examining new geological evidence, a group of scientists believes most of the dinosaurs were probably killed off in a matter of hours, not months or years as previously though:

Using estimates based on existing research, the five researchers calculated that the energy released by the asteroid strike was equivalent to that in 100 million megatons of TNT. The force of the impact would have thrown debris high into the air, much of it burning up while still in the atmosphere, the report said. This, in turn, would have turned the Earth into a giant broiler oven.

Yup, 100 million megatons. In computerspeak, assuming I didn't drop a decimal, that's 100 tera tons (as in terabytes). For comparison, the largest open-air nuclear device ever detonated was 60 megatons.

So, assuming further observations back up these predictions, it would seem the difference between survival and extinction was mostly determined by how well you could duck.