Labor Day weekend being crowded is a myth that has circled around for years. I've always suspected that it's folks that have never actually been there during that time that are perpetuating it.
Even still, this year was even lighter than past years. Gas prices and hurricanes seem to be the culprits. On Monday, you could practically walk on any attraction throughout the day. Sunday at MK got a little heavy in the afternoon, as did the Studios. Otherwise, it was super light.