I'm in Canada and we work in millilitres instead of ounces . . . but . . . my carton of egg whites says it contains 500 ml and is equivalent to 16 egg whites. Since 500 ml = 2 cups = 16 whites; simple mathematics would say that 1 cup of whites is equal to 8 egg whites.
Hope that helps.
And here we go for 2009 . . . Onward and Downward . . .