Judging Portion Sizes

Does anyone find it difficult to eyeball a meal and figure out how many servings of food you're actually consuming? I find it easy at home, when we've got a food scale and measuring tools handy. When eating out, however, it becomes more complicated.
My Lifestyle and Nutrition course linked to a portion sizes document that has some interesting ways to figure out how much you're eating- for example, one serving of peanut butter (2 tbsp) is equal to an amount the size of a golf ball. Helpful? Yes! Let me know if you've got some helpful hints to share!