SpaceX rates its chances of success with this experiment at no greater than 50 percent. But ... if it succeeds, the future of reusable rockets takes another step forward. Officials will not allow SpaceX to try this landing on land until the concept is proven at sea. If it doesn't work the first time, no worries. SpaceX will try again next year.
This will be a steering challenge. In the past, a 10km accuracy range was the best a Falcon 9 could accomplish. It'll have to be a lot tighter for this landing to take place. This reminds me of those old cartoons where a character has climbed to the high dive platform in a circus and the water pool waiting below was a mere drinking glass ... and a small one at that.
Good luck, SpaceX team. Here's hoping you make sci-fi a reality with this landing.
For more, see: http://www.spacex.com/news/2014/12/16/x-marks-spot-falcon-9-attempts-ocean-platform-landing
Update: 12/19: Date reset until early January when orbital mechanics make for better flying and so a pesky reading can be tracked down.
Update: 1/8/15: The Monday attempt failed when a reading came up faulty in the second stage. First attempt to retry will be early Friday, 1/9/15. Good luck SpaceX. Stick that landing!!!