The biggest problem that I have with Living Wills is that they are not revokable when you most need them so. Once you pass the power of your life or death into anothers hands you have given up all rights.
My lawyer was after me to sign one of these things. I told her I would sign one if it was time limited to one year, to be renewed or void every year on my birthday. She told me that that was a useless provision because if you failed to renew it, it would still have effect, no matter what language was used saying it was void after a certain date.
Reading this story makes me realize she's a pretty good lawyer, because she's absolutely right.
http://www.nrlc.org/euthanasia/willtolive/