Gliese 581d is a new extra Solar System Earth-like Planet discovered by Cnrs, the French Center For National Research. It orbits around Gliese 581 Star, without "d", at a distance right inside the Goldilock zone. The Goldilock zone is a zone around a star that allow the presence of Liquid Water. Its surface temperature is not so hot nor so cold to make Water respectively to evaporate or freeze. As anybody knows the presence of liquid Water on a planet is essential to develop Life. Almost in the form we know Life.
Gliese 581d has also a high density of CO2 in its atmospheare. It is likely, therefore, the presence of life in form of plant other than animal. Gliese is then a good candidate to be hosted by life.
Anyway Gliese 581d could appear a strange World if visited by Humans. The denser atmosphere and gravity twice that of Earth could make the new Earth a World different from our Planet.
The denser atmosphere absorbs light more than on Earth. If observed by Gliese surface therefore the sky will appear with a permanent red-sunset-like color. While the higher gravity would make all heavier. About twice.
With present technology it is almost impossible to arrive on Gliese 581d. It would take 20 years traveling at the speed of light, or 300,000 year with ours spaceships!
The following videos shows what we known about the Gliese "Solar" System.