We don't. My prediction then is only almost certainly true if we define habitable as a planet in a sun's habitable zone. However, I still think finding a habitable planet, per Unknowns's definition, is likely to happen by 2020.

http://www.npr.org/templates/story/story.php?storyId=101493448

If Kepler does indeed find hundreds of planets in habitable zones, that should get the popular imagination going enough for the successor to Kepler to be very well funded. Kepler Mark II in the air by 2017?