I personally believe in euthanasia for humans too Sue, I do think it is one of the few ways where we treat animals better than humans.
I personally have only had to make a quick decision with one of mine, and I know looking back that I did the wrong thing, it is the only one of mine where I look back and think that I should have done it differently - the others, the only thing I am guilty of is letting them go too soon, and I would rather lose days/weeks wtih them, than risk them suffering for 1 day too long. The one that I regret probably scoped the way I feel about the subject - she was my first cat on my own, and I had only had her for 9 weeks when she suddenly started fitting at 3am in the morning. My neighbours kindly got up and took me to the emergency vets, where they put her on morphine to see what happened. We visited her the day after, and the vet said that everytime they took her off morphine, she fitted again, there was a slight chance that by keeping her on it longer, she would recover (this was a 14yo who had had an abscess drained days before - vet said there was no connection though), but it was my choice. As I had no idea of what to do in this situation, I (foolishly) looked to my neighbour for advice, she is the kind of person who thinks that if there is a chance, however slight, they should be given it. Sadly, the cat in question died 'naturally' an hour after I left her, and that is something I do regret. I have since learned that my neighbour takes giving them a chance too far, and as a result, every one of the animals she has lost since I have lived next door to them have suffered - and sadly, I am not exagerating, I saw the majority of the animals on a daily basis and could see it, but the odd time I did broach the subject, it didn't go down well. I wish that vets could be frank with people and tell them that it is kinder for their animals to go peacefully with a jab than let them go for months suffering, as some sadly do.