Greg: Floyds (and Floyd licensees) were the only system that used a true "locking nut", as that was likely also a part of the Floyd Rose patents. Every other locking trem system used a behind-the-nut lock.
Much better control over the width, depth and spacing of the nut slots was possible and they could be customized to suit the fretboard radius or player's preferences. The disadvantage was that it was one more place where string slack could bind, so it wasn't as consistently stable as a true locking nut.
I still think the best locking nuts were the old Yamaha ones that were surface mounted and height-adjustable.