More reason to worry

Organizations interested in protecting Earth:
http://lifeboat.com/ex/asteroid.shield

Future Asteroid Interception Research allows you to donate via PayPal to pay for NEO interception work: http://www.fair-society.org/index.htm

http://gaiashield.com/myths.html contains a nice encapsulated summary answering many objections. Of particular interest is this:

MYTH: Asteroids less than 50 meters diameter will burn up harmlessly in Earth's atmosphere.
Most will burn up in our atmosphere and not actually strike the planet but that does not mean they will not have an impact. On January 18, 2000 in Canada's Yukon Territory a meteor (tiny asteroid) the size of a bowling ball exploded at an altitude of 25 km with a force of 3 kilotons. In 'burning up' in Earth's atmosphere it generated an Electromagnetic Pulse (EMP) similar to that of a nuclear bomb, knocking out the power over one third of the Territory. In 1908 the 50 meter NEO Tunguska Event generated a 10 megaton explosion 6 km above the Earth's surface (the altitude prescribed for military use of nuclear weapons to achieve maximum effect) flattening 2,000 square km of Siberian forest and incinerating more than twice that. However, no EMP was reported... It is estimated that a 1 megaton nuclear explosion (10% of Tunguska) 250 miles over Omaha would emit an EMP strong enough to collapse the economy and society of the United States from coast to coast at the speed of light.

A new study released last month revised the frequency of Tunguska size events upward by a factor of 2-3 to once every few hundred years.
http://impact.arc.nasa.gov/news_detail.cfm?ID=179

Other smaller, but not insignificant significant impact events occured in the Amazon in 1930 and Guyana in 1935, and Siberia impact in 1947. Consider how much of the world is untraveled oceans--we maybe get hit more often and not even know it.

A comprehensive Chronology of impacts: http://personals.galaxyinternet.net/tunga/I5.htm

And impact database: http://www.unb.ca/passc/ImpactDatabase/index.html

A NEO impact 13,000 years ago may have wiped out the Clovis Culture and many of the large mammals in North America:
http://www.eurekalert.org/pub_releases/2007-09/nau-rts092407.php
The evidence for multiple detonations comes from a four-inch-thick “black mat” of carbon-rich material that appears as far north as Canada, Greenland and Europe to as far south as the Channel Islands off the coast of California and eastward to the Carolinas... Evidence of mammoths and other megafauna and early human hunters, known as the Clovis culture, are found beneath the black mat but are missing entirely within or above it. This led the research team to conclude an extraterrestrial impact wiped out many of the inhabitants of the Late Pleistocene. ..The black mat was formed by ponding of water and algal blooms and contains carbon, soot and glassy carbon—remnants of burned materials. Some of these remnants are extraterrestrial in nature. For example, the research team has identified fullerenes, spherical carbon cages resembling a soccer ball, which are formed in shock events outside the Earth’s atmosphere. Trapped inside the fullerenes is a concentration of helium 3 that is many times greater than what is found in the Earth’s atmosphere. The black mat also has turned up nanodiamonds, which are formed in the interstellar medium outside the solar system, by or by a high-explosive detonation...The magnitude of the detonations would have been huge. “A hydrogen bomb is the equivalent of about 100 to 1,000 megatons,” Bunch said. “The detonations we’re talking about would be about 10 million megatons. That’s larger than the simultaneous detonation of all the world’s nuclear bombs past and present.”..Bunch says impact airbursts may be more common than previously thought with possibly two or three such events having occurred over the last 100,000 years. And more are sure to follow.