Lifeforce:
You know, I've been thinking of it, and experimenting with the barbell I've got out in the yard, and it's come to me that I've always done arse-to-grass deadlifts because that's what comes naturally, and as such, it's mechanically the most natural thing to do, as opposed to deadlifting from a poise midway between atg and upright (for a stiff leg deadlift, knees slightly bent).. the legs were designed to work atg, and since they're involved in the lift they should work as they were physiologically intended - it's for this reason we do atg squats, not because it needs more effort, but that's how the legs are designed to work. I don't see why it should be any different with deadlifts, it's still the same body and same legs you're driving with for the first half of the lift.
I've never actually thought of it in this way, the form videos I see all seem to be close to stiff-legged deadlifts (like the one semag posted), and since I tend to be the only guy in both my regular gyms who deadlifts (I kid you not - lol, it pisses them off when I take the olympic bar from the bench press to deadlift with, but no-one's asked me to stop so far), I haven't had a chance to think much about it.. I guess everyone's form is different (ever seen Ronnie Coleman deadlift?) but as long as it's safe then it doesn't matter I guess.