twice! Both times around DS's bday.
Last year, it was COLD! We ended up buying sweatshirts, hats and gloves one evening.........I think it was in the 40s, but there was quite a breeze and add rides to that..........we were freezing!
Another year, it was very rainy. That was the best! It would be cloudy all morning, and we'd do our EE..........then, just as it started getting crowded, it would rain for about 30-60 minutes. We'd duck into an indoor attraction, and when we got out everyone had disappeared! They'd show up 1-2 hours later. It was like an EXTRA extra magic hour!
So, all I want to add to what else has been said is to take advantage of the weather..............if it's cold buy sweatshirts and keep touring, and if it's rainy, buy ponchos and keep touring! It really cuts down on the crowds. When it's hot, and gets crowded, leave your EE park, take a break at the hotel, and then hop over to a different park in late afternoon..........that's when everyone else will be wilting and heading out.
Also, we always plan at least one day off in the middle of the trip. We go to downtown disney or other resorts for a relaxing change of pace.