Probably as we get better at detecting objects in space, we will know of more and more threats to impact. In the past, there have likely been plenty of "near misses" that we didn't even know about.
Asteroid YU55 is about 400M diameter and going to whiz by between the earth and the moon, on Tuesday the 8th of November.
http://neo.jpl.nasa.gov/news/news171.html
So this won't be a hit, but there could be some type of effects, especially as this will occur close to the full moon. In August, Comet Honda passed by and there were big earthquakes.
I did an analysis of Earthquake in proximity to previous encounters with Comet Honda, and the correlation was startling. That analysis is here.
http://oahutrading.blogspot.com/2011/08/comet-honda-causing-earthquakes.html
And as if we didn't have more to worry about than international banksters invading Hawaii and shutting down the main Highway (only Highway) at unknown times during a whole week, totally disrupting business so the banksters can travel freely between their luxury hotels 25 miles away to meetings in Waikiki, indeed this is true....
http://www.civilbeat.com/topics/apec-2011-hawaii-survival-guide/
As if that wasn't enough, now we have the largest sunspot observed in years, around 24 times the size of the earth.
SpaceWeather.com warns that a huge sunspot like AR1339 comes with a large potential for solar flares. The National Oceanic and Atmospheric Administration (NOAA) forecasts a 50 percent chance of medium-class M solar flares over the next 24 hours due to this sunspot.
Flares are also accompanied by flows of charged particles out into space, called coronal mass ejections, which can wreak havoc on satellites and power grids on Earth if they head our way.