Gliese 581-G is a planet we know nothing about other than it's a similar size to earth and a similar distance from it's similar sized star. You can equally say all these things about Venus, and, ironically, before a UGV was dispatched to Venus, a lot of people did. If you want to look it up, there are plenty of sci-fi novels from the early 20th century about life on Venus.
We now know however, that Venus is a complete hellscape, in every sense of the word. You've got yer fire (Venus is one of the most volcanic planets in the solar system) and yer brimstone (sulphur dioxide is one of the more common parts of Venus's atmosphere, comparable to the levels of carbon dioxide on earth).
On the subject of Venus, another thing that's gets me is that reporters are all calling this the "first planet found where life similar to our own could flourish", which is complete malarkey. There's fossil evidence that life has existed on Mars, and a popular theory (well, not that popular, but it exists, and I personally believe it's worth considering) is that life on Earth actually originated on Venus 4 billion years ago (not as in the way, that 4 billion years ago aliens from Venus colonized Earth, that's just ridiculous. But microscopic lifeforms can be ejected from a planet by, for example, volcanic activity). Never mind the fact that it's strongly theorized earth-like life could exist on any of the Jovian planet's moons, or, indeed, on the cloud layers of Jupiter itself. Perhaps not complex life, but microscopic life, definitely.
But I'm ranting. It's an interesting find, that's for sure.
