I have with strange results... on both sides of the coin.
I had car trouble and waved down a car...the man stopped and looked at me carefully, "I guess you look safe enough".
I'm a woman. not that it means women are safe to pick up, but it surprised me at the time.
I picked up a young man in death defying cold weather who was hitchhiking. I even turned around to go back and get him. He'd been on the road for 15 miles. Was traveling another 100 miles on a Friday to spend the weekend with his girlfriend. Hmmm...now that's food for thought.
I took him to the nearest convenience store to warm up and as I left he turned right around and thumbed for a new ride.
I ran out of gas...and was picked up by a stranger. Another who seemed suspicious of me... He left me a few short miles down the road at my destination.
On the same road, a few years later, a trucker was down. I had a friend with this time and we picked him up and took him to the nearest truckstop. Kind of unappreciative as a note of remembrance, but otherwise unnotable.
That pretty much is my experience. I live in a small rural area...and so many of these were examples from that area. I don't know, to be honest, how I'd react in a larger metro area. My heart goes out to the homeless, for example...but I don't know how to interact with people I can't identify with. i've been blessed in that area thus far. Any insight there?