The Hammer Strength unilateral supinated-grip pulldown is one of my favorite machines. It's nearly impossible to duplicate with free weights what this machine can do.
Several training methods work great on this machine, like maximum tension alternating pulls (hold one side isometrically in the contracted position at the bottom while the other side is moving). It also works great with bands for added accommodating resistance.
We all know building a muscular body takes time, but if you want to speed things up and kickstart some serious hypertrophy, you must make intelligent use of two core muscle-building concepts: absolute strength and absolute volume.