I made a quick and lovely soup with some leftover chicken stock, with a recipe from Laurie Colwin's wonderful book, More Home Cooking (it is a sequel to the obviously titled- Home Cooking).
It involved stirring a beaten egg in to the stock and adding the juice of a lime, then whatever you had in the house.
I saw something similar on the menu at a Greek restaurant. Is there any connection? I guess it is also related to the infamous egg drop soup from Chinese restaurants.