Record-Setting Asteroid Flyby, named "2012-DA14" is about 50 meters wide and probably made of stone instead of ice or metal. The average flyby is about every 40 years, although this one is pretty close. An asteroid stikes the planet about every 1200 years or so. A similiar size object formed the mile wide crater in AZ, made of iron it was a hard hitter 50,000 years ago.
Passing approximately 17,200 miles from earth, THIS ONE WILL NOT HIT EARTH. It will be passing through "Low Earth Orbit" where the international space is, and "Geostationary Earth Orbit" where weather and telecommunication satalites orbit.
Visually speaking, from earth the asteroid will appear to be moving about twice the width of the moon ever minute. If you're a skilled sky watcher, you should be able to catch a glimpse of it with your backyard telescope.
You can sign up to "Spot The Space Station" and recieve an email alert when you will have a fly-over by going to http://spotthestation.nasa.gov/ and signing up.