I always thought this was a country based thing. Brits use a knife and fork usually, my mum's South African friend told me that South Africans don't, they just cut and put the knife down, I noticed this is true of Americans and Brazilians too. I haven't analysed any other nationalities
Going to strongly disagree here. I am in SA, and I don't find that accurate. Knife and fork are very normal behaviour, in fact, if I were in a restaurant and saw fork only eating, I was be a bit surprized. I can only think that your mums friend is referring to when at a braai (bbq) where then, picking up the meat and getting stuck in, is then the normal. (Think meat on bone, chicken, ribs etc). In my cutlery drawer, I have two sections for knives, one are normal day to day ones, and the other are the steak knives (excluding chopping, slicing, dicing knives)
My dc eat burgers with a knife and fork if were are in a restaurant setting. Pretty normal behaviour.
But then again my mother always told me I was brought up by the queen. Yes mum, it must be true 
(Hope this is still a lighthearted thread)......