I've started doing 20 rep deadlifts because I feel I get a better workout from them if I go into the higher rep range - it's good for improving cardio somewhat and it's a good test of how strong your mind is - there's a tendency to want to quit after 12 reps or so so you've got to fight it to keep going. Besides, I'm not very strong on deadlifts anyway and there's no point in me struggling with 400lbs + if all I'm going to get is four or five reps in a set.
Same for hamstring and calf work too - usually do between 15-20 reps a set for all related exercises and certainly never go below 12 reps in a set.
