My cousin in the Netherlands chose euthanasia after his stomach cancer came back and became terminal. He had a large family and he wanted to give them time to say goodbye. Here in Oregon it's also legal; the Oregonian newspaper did a special feature in 2007 on one of their researchers who chose assisted suicide:
Lovelle Svart - Living to the End - The Oregonian
I believe it's a personal choice, and it's not my place to say whether or not another person should keep living. I couldn't say for myself whether I would choose it or not, as I think it's a bridge you have to cross when you come to it, but it's nice to know it's a choice.