Are you referring to riding ACA's Atlantic Coast route or riding down the east coast in general. If the former, I don't think it matters much, at least not for the part above the D.C. area. That's because the route isn't close to the actual coast in most places. (Don't know about south of D.C.) Now if you are talking somewhere like the S. Jersey shore, most days the wind blows roughly south to north. Yesterday I finished a three day trip by riding north along the coast from Ocean City to Atlantic City to catch the train home. Had the wind at my back the entire way. When I stay down there and ride I typically go inland in the morning, ride south and then head back to the coast to take advantage of the typical tailwind going back north, which tends to pick up as the day goes on.