What is your opinion on shock collars? Do you use them?

I hear a lot of negative opinions on shock collars, but when I looked into them they don't seem that bad if used properly. Trainers who use shock collars describe the shock as rubbing your feet across the carpet and touching something. I hear a lot of people who use them say they test the level on themselves first. Do you think they are a good training tool? Why, why not? For those who have tried them, what did you use them for and did it work? Would they help with running away or chasing animals?

I'm referring to the remote collars, not the invisible fence or bark collar. I do not use them, just looking for information.

Thanks