In 2005, Congress asked NASA to create a plan to track most killer asteroids along with methods to deflect the potentially catastrophic ones. In March of 2007, NASA released a report, which basically said that this task was too expensive, so it would not get done. Due to insufficient funding by congress, NASA Can Not Pay for Killer Asteroid Hunt.
The second triennial AIAA Planetary Defense Conference was held March 5-8 at George Washington University, Washington DC. Pete Worden (Director, NASA Ames) opened the conference by stressing the importance of NEO studies (surveys and characterization), but he also cautioned that while we may have the technology to largely eliminate the impact threat, NASA at present has no budget to expand its NEO program beyond the current level of approximately $4M/yr.
"We know what to do, we just don't have the money," said Simon "Pete" Worden, director of NASA's Ames Research Center.
There have been numerous frightening encounters, including Apophis, which will pass by inside the orbits of TV and communications satellites. Some have feared that this pass will affect its orbit enough to cause an impact on a later pass in 2036, but as of now, we are told the odds are quite small (See Torin Scale).
Recently, we have learned of an asteroid poised to possibly strike Mars during January, 2008. Some have compared this impact with one in Tunguska Valley Siberia in 1908.
The bottom line is that although NEOs (Near Earth Objects) pose a threat, we a re not likely to see any action in the near future. The report to congress details current programs, recommending they continue as currently planned as NASA attempts "to achieve the legislated goal within 15 years. However, due to current budget constraints, NASA cannot initiate a new program at this time."