pssh......We used to hold onto shock collars and skate down the driveway towards the street, right through the barrier and it was a lot of fun. Not at all was it some sort of prolonged pain, and isn't much different than shocking yourself at an outlet. Don't know that shock collars are necessary training devices, but I don't know that they're necessarily cruel, or at least not as cruel as some are suggesting. Further, most dogs pick up on the function of the collar very quickly, and most don't need to be shocked beyond the learning period.
Again, before I'm attacked, I don't think the collars are essential—or even necessarily the best method—in training a dog, but they are not some horrifically torturing and cruel device. I worked as an electrician's apprentice and was shocked regularly and it's nothing more than momentarily painful and startling/surprising.