LAST EDITED ON 02-12-13 AT 01:33 PM (EST)Make no mistake about it, there are astrophysics scientists who have devoted their entire academic careers and lives to this very subject, writing books on it.
We're probably good for a few centuries at least, barring any unexpected and still yet unobserved perturbations in solar system dynamics.
Surfkitten Summer sigshop 2008
The movies are good in making us aware of the potential danger and its possibilities, but they are poor in dramatizing the actual response of an impending event. Rather than blowing up an asteroid, which may exacerbate the situation, a gentle nudge well in advance is really all it takes to make a potential impact a wild but harmless fly-by. The current rock is going to have its solar system trajectory majorly altered by it's near Earth fly-by.