I'm sorry, Suja. I think that as long as he isn't in a lot of pain all the time, and still enjoys his life over half the time then there isn't anything wrong with choosing to keep him alive. He's got all the great things a dog wants - food, naps in the sun and other dogs to interact with. I would also measure it, too on if the dog/cat stops eating. That tells me they aren't interested in being around much anymore.
Chrissy - the theft accusations were so awful. In 5th grade, someone from my girl scout troop stole my girl scout cookie money on the day we were supposed to turn it in and the troop leaders accused me of spending it. In 8th grade I was a page at the state capital, so one of 15 or so 8th graders in a small class and someone stole money from someone else and put it in my wallet so it would look like I stole the money. It was so terrible I couldn't believe it - I still feel like no one believed me, even my mom. And then my first job out of school I had a co-worker who told several volunteers with our organization that I stole money so that I should never be allowed to handle money. I got her fired soon thereafter because I caught her doing work for another organization using our copiers/paper (essentially stealing, so hoisted on her own petard.) I guess I have been hanging around the wrong kind of people.
"Any idiot can face a crisis; it is this day-to-day living that wears you out." -Anton Chekhov