Chimeric embryo experiments are highly controversial; they're easy to confuse for some kind of Dr. Moreau-type madness, but even when you've got a grip on what's actually going on, it's hard to take a firm stance on either side. On the one hand, you could well cure forms of diabetes, grow hearts or kidneys or any other organs, and legitimately save lives. On the other hand, this is wild, foreign stuff, and also involves some genetic manipulation and almost certainly some inhumane treatment of animals. (How happy are those pancreas-less piglets, really?) It's a debate without easy answers, but one we'll be following closely.