We stayed at Pop Century this past Dec. during Pop Warner week and aside from seeing a couple of large groups of kids all dressed the same in a couple of parks we otherwise wouldn't have even known they were there.
If you are looking for a time to avoid visiting WDW then stay away during Jersey Week. We made that mistake in 2004 and the ride lines were like they were during the summer months. I think EVERYBODY from New Jersey was there. lol