I know you have to keep the barbell close to your body and your knees slightly off lock, but I don't feel that stretch in my hamstrings even if I go pass the knees even as low as the shins. I don’t have a raised board to stand on to get a deeper stretch as some people say. Now I find if I hold the barbell away from my body “not running down the legs” as my torso bends I feel a deeper stretch in the hamstrings which when taken to my max rep they are throbbing. Question is although not right form as the video link states I still feel a better hamstring performance by doing it the way I mention. So if I not doing this exercise the way you are suppose to why do I feel a better stretch and will I suffer any back problem from doing it that way?
Here’s a video of correct form
http://www.youtube.com/watch?v=OpzRX3slWjE

