Being a Gold member for the last 3 years, I have only been upgraded once with Air France, a mere upgrade from economy to Tempo Challenge from Marseille to AMS.
However with KLM I have been upgraded many times. It seems like their 747 flight between Mexico and Amsterdam is always overbooked, even if they dont upgrade you to the real business class upstairs, they put you in a business seat (rows 1-4) with economy service
Another frequently overbooked route(at least summertime) which I have been upgraded on some times is between AMS and Sao Paulo.