Asteroid Close to Earth November 2011?

I heard that there is an asteroid that is so close to earth in November 2011 that will probably collide with our planet.
Is it true that this big asteroid is very dangerous and can cause a lot of damage to the earth because it is close?
Why are they telling us about it now in November 2011 and not before so we could be prepared?
I'm really scared the asteroid may possibly hit earth and start a major extinction just like it happened with the dinosaurs.

The asteroid was close but the danger is over.
The 1,300-foot wide asteroid missed Earth tonight in the closest encounter in more than three decades.
The asteroid often travels in the vicinity of Earth, Mars and Venus, but NASA says today's encounter was the closest it has come for at least the last 200 years.
The asteroid, named 2005 YU55, came within about 325,000 kilometers of the planet Tuesday evening.
During its closest approach, which occurred at 6:28 p.m. EST (2328 GMT), it was inside the orbit of the moon.