A hundred years ago a large meteor exploded ten kilometers above the Earth's surface in Tunguska, obliterating 830 square miles of woods. It was the largest impact in recent history, but nothing compared to this.
The meteor—or comet fragment—was only a few tens of meters in diameter, according to modern estimates based on its 15 megatons energy blast. This 3D simulation, however, shows what something like Apophis will do if it hit Earth. I saw it a while ago on the web, but now it is available in glorious HD, so you can see all the gritty-nitty detail of good old planet Earth getting completely obliterated.
The fact is that these things are very real, and they are lurking out there. So with that in mind, keep your list of things to do before you die handy. You never know what awaits for us in 2009. [YouTube—Thanks Louise]