I read a story a few days ago about an asteroid that came closer to the earth than some geostationary satelites sit in space, and they didn't see it until it was upon us because it came from the direction of the sun, in a "blind spot". So at least they saw this one you guys were talking about 20+ years out!
Story here:
http://www.space.com/scienceastronom...se_041222.html