On November 20, 2007, NASA-funded observers discovered an asteroid, subsequently named 2007 WD5, after it had made its closest approach to Earth at 4.7 million miles. In terms of NEOs (Near Earth Objects), this is a very close call.
While we may be out of the woods, Mars certianly is not. At 5:55am EST on January 30, 2008, it is scheduled to pass within a mere 30,000 miles of Mars. This means there is at least a statistical probability of 1 in 75 that it would collide.
This would be an event the size of Tunguska, or larger. It would slam into the surface at more nearly 28,000 mph, create a crater more than a half mile wide, and release more than three megatons of energy.
On another note, notice that the asteroid was discovered after it made its closest approach to Earth. We need to do better than this NASA; you're gonna let another Tunguska or dinokiller through.