In an address to the UN recently, the Association of Space Explorers pleaded with the international body of leaders to develop an asteroid impact plan so that if we see one coming, the world can pool its resources and come up with an answer before it strikes.
Sure, it's been 65 million years since an impact supposedly removed the evolutionary cul-de-sac known as the dinosaurs, and just recently there was talk about the Apophis asteroid, which in 2004 was said to have a 1 in 37 chance of hitting the earth. It was later refuted with more research but it is certainly a reality that we may need to face someday.
NASA is watching 209 "near earth objects" and the advancement of telescope technology is moving at such a clip as to create newer and better ways to survey the sky for moving objects. Still, Astronaut Rusty Schweickart of the Apollo 9 mission stated that, "Until we have a response in place, we're as vulnerable as the dinosaurs."