This is an article on synthetic biology in The New Yorker. I haven't read the whole thing yet, because it's long-ish (eight pages of a narrow column, which I hate reading on the screen - I don't mind narrow columns in actual newspapers or magazines, but on-line, it's freaking annoying).
In the little blurb under the illustration on the first page, it says, "If the science truly succeeds, it will make it possible to supplant the world created by Darwinian evolution with one created by us." Now, I don't entirely agree with that statement. I've said before that I think the idea that things man does are not natural is wrong. It would still be a world created by evolution (if, in fact, it was "created" by evolution in the first place). If you're going to suggest that there's something special about humans, in that things we do are not natural, then you probably shouldn't be using words like "evolution."
Anyway, the idea of synthetic biology scares the crap out of me. When Dolly was announced to the world, I was one of the people who had to sit down from the horror of it. It's interesting, and the applications could be marvelous, but I think the higher you climb, the more certain and the more painful the fall will be.
For instance, when I first got into botany, I thought, "Wouldn't it be cool to do photosynthesis artificially?" Not just as in Nobel Prize-winning cool, but because think of what that would do for our atmosphere!
Of course, there goes one big reason to not go into full-blown deforestation mode. Who cares about the rain forests anymore? Who cares about the oceans' phytoplankton (which organisms actually do more converting of CO2 to O2 than all the angiosperms and gymnosperms combined)? We can do it ourselves!
I try not to get too worried, though, because no matter what the scientists in their infinite wisdom do, they won't kill Earth, short of building one of Tesla's machines that would crack the planet into pieces. (And who says one or more of those pieces wouldn't manage to survive somehow?) They'll just make it inhospitable for humans and a lot of other species, triggering a large die-off, making room for a new speciation event.