Thanks for posting that. I was trying to recall the details. I love the part about being detected AFTER it passed by.
And things have hit the earth before with dire results-end of the dino's was probably due to an impact. Of course, that one worked out okay for us!
Even with all of our technology, robotic computerized scopes, professional observatory's, thousands of high end amateur scopes, satellites, and imaging techniques, an asteroid could still impact this planet without being detected first. Even a large asteroid could surprise us, however, the larger they are, the more likely they would be detected in advance. How far in advance is anyones guess.