Had to add another NASA gem :)

A new statistical study of planets found by a technique called gravitational microlensing suggests that Neptune-mass worlds are likely the most common type of planet to form in the icy outer realms of planetary systems. The study provides the first indication of the types of planets waiting to be found far from a host star, where scientists suspect planets form most efficiently. Contrary to some theoretical predictions, the most numerous cold exoplanets have masses similar to Neptune, and there doesn't seem to be the expected increase in number at lower masses. Lead scientist Daisuke Suzuki, a post-doctoral researcher at NASA's Goddard Space Flight Center in Greenbelt, Maryland, infer this from current detections. The team concludes that Neptune-mass planets in outer orbits are about 10 times more common than Jupiter-mass planets in Jupiter-like orbits. Gravitational microlensing takes advantage of the light-bending effects of massive objects predicted by Einstein's general theory of relativity.

Read on, it's well worth the effort. :)