The actual Science paper was interesting, although the scientist presenting this over-stated their findings (in my opinion). I think they still have some explaining to do, which I hope they get to and confirm that, indeed, these bugs use arsenic (As) instead of phosphorus (P).
In the paper, the microbes grown in arsenic but no phosphorus conditions (As+/P-) actually still had 2% dry weight P in them (and As was 20% dry weight). So they haven't proven that they don't need P at all. It would be a very cool find if they do prove this, since phosphate is thought to be /required/ for all life (same with carbon, nitrogen, oxygen, hydrogen, sulfur).
Also the microbes grown in Arsenic conditions looked like they were about to explode their guts out. See artist's impression above.