This paper, http://arxiv.org/abs/1311.6806, discusses Kepler mission results. The authors deduce that 5.7% of sun-like stars have an earth sized planet orbiting in the habitable zone. That is a shockingly large number, IMO. Considering there are an estimated 26384 class G class stars within 324 light years of earth [re: http://www.astronomycafe.net/qadir/BackTo110.html], that means there are about 1500 earth sized planets that orbit in the habitable zone of class G stars within 324 light years. The study considers both class G and K stars as sun-like, so the number of such planets should more than double, since class K stars are even more come common than class G stars.