yeah, I have done them a lot in the past, you can vary the height of the box depending on what you are trying to work, higher for hamstrings and lower for quads.
I also have done them overhead as a variation, and in a clean rack position.
I used to do them regularly. Then I stopped b/c squats would wipe me out and I'd be too dizzy to risk it! But thanks for giving me an idea on what to do while I lay off squats for a while (Heresy, you say! But I'm having some knee problems).