This could end very badly...
Artificial letters added to life's alphabet - tech - 30 January 2008 - New Scientist Tech
Two artificial DNA "letters" that are accurately and efficiently replicated by a natural enzyme have been created by US researchers. Adding the two artificial building blocks to the four that naturally comprise DNA could allow wildly different kinds of genetic engineering, they say.
Eventually, the researchers say, they may be able to add them into the genetic code of living organisms.
This just strikes me as something with potentially awful, unforeseen consequences. As Mark Shea is fond of saying, the history of the human race can be summed in two sentences "What could it hurt?" followed by "How was I supposed to know?" This falls into that category.
Hat Tip: Slashdot