I think that boiling chicken too much should be on the very bottom on your list of concerns. I'm always much more concerned about roasting my food too much on the grill. I usually pan fry my steaks these days though. Or I'll just sear the surface of it and toss it in the oven.
Unless you cook the shit out of your chicken you should have no concerns about losing any nutrients at all. I put my chicken breasts in a skillet with a tiny bit of oil and lots of water. I also toss some soy sauce on it when its almost done. I've heard Dave Palumbo talking about that too. I know what my health's like and don't have to be too concerned about sodium, especially considering how clean my diet is. But if you're concerned about sodium or dieting down for a comp, I'd skip the soy sauce unless you use a modest amount.