The older, larger zucchini tend to be less flavorful than the smaller squash, but any bitterness comes from environmental factors (moisture or temperature). So small or large squash can be bitter. The large squash are still fine to use, but might be best shredded in cakes or breads. It will not freeze well due to its moisture content. See the May/June 2010 issue of Midwest Living for a whole page of usage ideas for zucchini.