I finally saw the policy enforced on a MEL-SYD flight one Thursday afternoon. Interestingly they only tried it on passengers who were NOT clearly lined up in the Platinum/Gold lane. Quite a few passengers were approached in the waiting/holding pen, their luggage weighed and then checked in.

However the worst offenders are always among the Platinum/Gold pax who routinely struggle on board with two or three pieces of hand luggage (as a Plat myself I see it all the time). The worst are those women who struggle with trying to put a way-too-heavy case in the bin and then ask a man to help them. That's just outrageous IMHO