Recent Controversies in Astrobiology
Arsenic life.
The story. In December 2010 Felisa Wolfe-Simon et al published a paper in Science saying that they had found a form of life on Earth that used arsenic in place of phosphorus in some molecules, notably in DNA. This created a storm of protest, for many reasons. Chemists said that arsenic-containing DNA (of the sort Wolfe-Simon et al claimed) was unstable when dissolved in water. It just would not happen. Biochemists and microbiologists were more inclined to believe the basic idea, but throught that the evidence presented for arsenic-DNA fell far short of proof. In May 2011 Science published some of these objections (notably the original paper remains free for anyone to download, the objections and commentary need a subscription to read).
My take. It is pretty clear that GFAJ-1, the 'arsenic bug', is unusual, but its properties are within the range of organisms known to grow in arsenic-contaminated environments, and almost certainly it does not use arsenic in place of phosphorus.