i should also add that in american recipes using cups, the traditional way to measure flour is by using the 'spoon and sweep' method. This sounds fussy, but it really the only way to measure if you are baking and want great results. so, as the previous poster said - all measures (tbsp, cups) should be level. but with cups, you should measure flour by 'spooning and sweeping' - which means that you lightly spoon the flour into the measuring cup till it is heaping, and then level off the flour with a knife. if you simply stick your measuring cup into the flour and then shake to level it off, you will indeed be using more flour than if you spoon and sweep - thus altering the recipe and possibly ruining your results.
remember - spoon and sweep is only for measuring flour in cups. don't worry about measuring other ingredients, like sugar.