I have stopped several times, and normally do as long as I'm alone and not in a hurry. Always have. I genreally dont stop unless I see kids when I have the lady and/or the baby with me though.
When the optispark distributor died on my Caprice, I was 20 minutes from home. A 20 minute drive is a heck of a walk. I could still see my car when a couple in thier late 40s picked me up, and I look like a hell's angel. A while later, the same car, the battery cables shorted, melted the terminals off of the battery, I got a ride back to the range, where I borrowed a vehicle to get to the hotrod, steal the battery, and get back to my Caprice. Someone let me use their callphone when the fuel pump went out on my dakota, they offered me a ride, but Mom didnt live too far away. When a bearing went out on my alternator, so I took it off and started walking to the parts store. I didnt walk far, got a ride to and from, and he stayed until my car was running.
I offered payment to all of these people. They all refused. The only time payment was made was when I borrowed a truck from someone at the range, he wasnt there to stop me from putting gas in it.
I once stopped and picked up a guy who was walking towards traffic on the shoulder. All the alarms were going off in my head based on his looks, but I stopped anyway because so many people have for me (despite my simular looks). Turns out, two miles up the road, his wife and two children were in a Pontiac Parisinne(sp?) that had a flat spare. They had a flat the week before as well, which is why a flat spare was such a big deal. So I traded spares with him. Watched him change them, he refused to let me do it. He didn't refuse the cordless impact gun I offered though. As I was tossing my new flat spare in my trunk, he offered me a $20, instead I got a handshake.