This stretch is a very popular hamstring stretch that is very effective on releasing tension on the hamstrings.  Because it is one legged, you are more focused oppose to stretching both hamstrings at the same time.  It is very important that the hips do not lift up from the floor, so your main priority is keeping both sides of the hip in contact with the floor to efficiently stretch the hamstrings.

The Standing Hamstring Stretch is a very effective stretch when done correctly.  The most common mistake that people do is locking the knees (hyper extending) and putting unwanted pressure on the knee joint.  When stretching, be sure to hinge from the hip joint so all the tension is on the Hamstring oppose to the lower back.  Stretch to the point of tension, not pain!

This is the standard hamstring stretch that is used and highly recommended for tight hamstrings.  If you're suffering from tight hamstrings, the Seated Hamstring Stretch would be your best bet - but to successfully elongate the hamstrings, you need always remember to hinge from the hip, and not to let your back round in.