A little perspective here to those that say YU55 is the size of an aircraft carrier. Imagine a toy aircraft carrier in a gumball machine... YU55 is the size of the round plastic container the toy came in, not the size of the toy itself as YU55 is semi-ball shaped.

A little more perspective... YU55 is approx 1300 feet or 400 meters...

The meteorite that made the HUGE crater in AZ was estimated to be 130 feet or 40 meters...

pic - [link to farm5.static.flickr.com]

so... if we scaled down that 130 foot AZ meteorite to the size of a large marble (shooter) and did the same for the 1300 foot YU55, we have something about the size of a bowling ball.
Now scale back up to a 1300 foot rock ball screaming toward earth and our moon at 30,000 MPH... how fast is 30,000 MPH? In 2005, YU55 was around 1.5 million miles away...