On average, Earth receives one major impact about every 60,000 years or so, which means that by the Gaussian distribution standard, we're waaaaaayyyy overdue. Granted, it's an easy argument that these events don't follow a standard, and so averages are a bit pointless here. Nonetheless, even with Jupiter in the way and most big rocks confined to the belt, it's still a matter of when rather than if. The only real variable in this equation is our level of preparedness. We've got all our eggs in "one very fragile basket".
I find it troubling how people truly have faith that, for any problem or potential problem, there's an expert diligently worrying away at a solution - not only competently, but with the proper tools. This, my friends, is a scary mindset, because it justifies apathy. Too much faith in our very shaky foundations? Bad, bad, bad.