SpaceToday.net has a good summary of the recently discovered extra solar planet massing only five times as much as ours.

My recommendation for the planet finders is to start looking for wobbles on the wobbles of the super massive planet orbits to see if they can find smaller planets or Moons. Or wobbles on cold binary stars that circle near the hab zone of hotter primaries that may also turn up lower mass planets.

Even if we never directly detect low mass planets, big hab zone planets may be like Jupiter or Saturn and have lots of moons, some of which have comfortable gravity and an atmosphere.