Paul Gilster over at Centauri Dreams has written a post about the prevalance of small, rocky worlds in our galaxy. He reports on 45 new planet reports revealed at the International Astronomical Union's meeting in Boston which have yet to be confirmed, one of which includes a planet projected to have roughly four times the mass of Earth. If confirmed, that would be the smallest exo-planet found yet.
Even if not confirmed with exactly those specifications, these findings provide more information about the universe around us. The planets were found using the High Accuracy Radial Velocity Planet Searcher at the European Southern Observatory's La Silla 3.6m telescope.
And if you read the post at Paul's site, you should also pay attention to the comments. Several of them are highly insightful.