This was the question from one of my students, about the whole Arsenic-using microbe thing. The answer is "no." I didn't really think so on a casual read of the paper, and a bit more thorough read makes me even less sanguine.
The authors really needed to do a bit more chemistry--as they noted, the cells still contain phosphorus, and some patient calculations (by people who weren't busy with the final week of the quarter) suggested that the amount of phosphorus is enough to sustain a somewhat unhappy cell. Indeed, that's the most vexing thing--even after many generations of passage, there was still phosphorus in all the cells, leaving a lingering doubt throughout the whole project. More rigorous chemistry procedures are required. It's necessary to do the hard work to make really phosphorus free media, and really really purify the DNA and small-molecule fractions so there's no chance of random cellular arsenic contaminating an otherwise normal sample. So, there's stuff to be cleaned up, and it can and should be cleaned up. I think that the authors' claim is still possible, but more proof is necessary.
It's been interesting to see how various blogs have treated the story--generally, not nicely (see here, here, and here for a few, including John Roth and Jonathan Eisen here at Davis). Part of the issue has been the lack of necessary rigor. But I think people have been especially eager to hit this story because of how it was presented: this was the classic case of science by press release, with a one-week-long drum roll leading to the reveal. That's just asking for it. While newspapers love science by press release (it saves thinking), most bloggers (who are more scientist than journo) hate hate HATE science by press release.
UPDATE--14 December. I just spent the weekend at the West Coast Bacterial Physiologists Annual Meeting. This was not mentioned once--an index of how much regard it has gotten.