Gliese 581C is believed to be approximately four times the size of Earth and calculations show that its orbit is within the habitable zone around the star Gliese, a red dwarf star seen from Earth in the constellation Libra. 581C is much closer to Gliese than Earth is to our own Sun, so I would expect it to be geologically quite unstable as a result of the gravitational forces exerted upon it. Astronomers believe that the surface temperature on 581C range between 32-104 Fahrenheit which makes it comparable to our own planet in temperate terms but there are some vast differences.
Whilst 581C is large enough to retain its own atmosphere nobody knows whether it actually has one because retaining an atmosphere requires gravity, and gravity is dependent upon the rotation of the planet. Retention of water on the planet surface is likewise dependent upon the forces of gravity and water is essential to life as we know it. We also have no idea what the level of solar radiation is like on the planet surface which is again dependent upon the retention of a suitable atmosphere. 581C is certainly on the move at great speed around Gliese, apparently orbiting in 13 days(!) so there is absolutely no chance of any seasonal variation if the planet is revolving fast enough on its axis to create enough gravity to retain its atmosphere and its water.
As we cannot physically see the planet in any way it impossible for anyone to say with any conviction that the planet is actually inhabitable. Reports of "fuzzy images" are just complete bunk. The existence of 581C is only known due to measurements of tidal "wobbles" in the star Gliese. Actually being able to see the planet with a conventional telescope from Earth would be almost impossible. The next generation of Space Telescopes may be able to see planets like 581C but for the time being we can only make educated guesses and mathematical predictions based around observations of other phenomena.
It would be nice to know we are not alone in the Universe as we know it and it is without doubt a pretty arrogant assumption to believe that we are. If the Geneva Observatory in Switzerland has truly discovered a potential home for ET then that has to be a good thing but there are some things to bear in mind. Gliese is an old star, much older than our own star. Any civilization existing on 581C is likely to be much older than our own civilization and its technology is likely to be way ahead of anything that we currently have. The SETI institute have already searched the Gliese system twice for any signs of life using the Parks Radio Telescope in Australia during 1995, and again during 1997 using the Greenbanks Radio Telescope in the USA, both times finding nothing so we still have an open book.
581C is believed to be the most "Earth-like" planet discovered so far but for the time being the search for extra-terrestrial life goes on. Personally I feel that there are much more exciting discoveries waiting to be found within our own star system, particularly on some of the moons around the gas giant planets. We shall just have to wait and see what the Universe decides to reveal to us when it thinks we are ready.