image via Martha Stewart
Any utensil specifically reserved for your own use (ie. fork, spoon, knife within your place setting) should never dip into a communal dish at the table. The serving utensils, like the huge spoons that look like what a giant would use to eat his soup, placed at each dish are to be used for serving out of communal dishes and on to your plate when a family-style dinner is served, regardless if the dinner is held in your home or a banquet hall.
Even amongst immediate family, a utensil that has already gone into your mouth shouldn't never touch someone else's potential serving.