Apparantly, there have been several close-calls over the past couple of years of meteors almost hitting the earth. Big ones that can do a lot of damage. And basically, there's no real system set in place to watch out for this stuff.
I say apparantly, because this is second-hand information, and I can't back it up with a link or anything.
Somewhat related is this awesome podcast (thanks Paul): The Skeptic's Guide to the Universe