According to an article in Wired, researchers at Beijing’s Tsinghua University have developed a plan for diverting Apophis before it enters that 600 mile-wide space "keyhole" that will turn the asteroid back on itself. The plan is to take a solar-sail satellite already in a retrograde orbit (as most are, to slow them down) and allow it to orbit directly with the planet, significantly speeding it up. The researchers believe that the 10 kg satellite, given a year of lead time, will successfully impact the 45 million ton, 1,600 foot wide asteroid with significant enough force to divert it from passing through the keyhole. (At that point Bruce Willis and some grease monkeys will jump out of the satellite, blow up the asteroid, and save the planet)
However, astrophysicists with the European Space Agency want to do one better, saying that Apophis provides a low-danger opportunity to study asteroid impact for future near-earth asteroids. The probability of Apophis actually impacting either Earth or the moon was downgraded by NASA in 2009 to a 1 in 250,000 chance. That said, your chances of winning the lottery are 1 in 14 million. The proposal, called the Impact Mitigation Preparation Mission (nicknamed Don Quixote) would send two spacecraft toward Apophis, the Orbiter and the Impacter. The Impacter would collide with Apophis to divert it from Earth's gravitational "keyhole", while the Orbiter would stand by to study the effects. The Orbiter will study trajectory and behavior prior to impact, and immediately after impact, and may provide clues on how best to manipulate future impact hazards. Seats on the Orbiter are selling like hot cakes. Seats on the Impacter, not so much.
Apophis was, at one time, rated the highest ever on the Torino Impact Hazard Scale (a four), the only scale to measure the relative threat of space bodies actually impacting with Earth. However, in 2006 the likelihood that the asteroid would actually hit the moon or Earth was downgraded, and again in 2009 (to a one). In 2013 Apophis will be passing within 9 million miles of the planet, allowing scientists to better calculate how 2029 and 2036 might shake out. In any case, it could provide the TV shot Mythbusters with their highest rated episode yet (assuming they're still crashing stuff in 18 years).