Awesome Fresh Air show yesterday with Dr. Nancy Kay, author of Speaking for Spot, about being a good medical advocate for your pets and making the tough decisions on their health care with so many more options, often expensive, available:

http://www.npr.org/templates/player/mediaPlayer.html?action=1&t=4&islist=true&id=13&d=03-19-2009

This is a book I'm going to pick up.

EDIT: This includes a very good description of pet euthanasia and what it's like for a veterinarian/vet tech who is participating. As part of my job, I'm in the process of being certified for euthanasia and I found myself nodding along with her as she spoke. She also talks about making the choice to euthanize an animal and her experience corresponds with my experience. I've heard from probably over one hundred people who regret delaying the decision and from only one who felt they had done it too soon (and in that case, after hearing about the condition of the pet, I think they made the right decision, even if they don't.)