We took our daughter the week before she turned 3 months old, and again at 3.5 months. The 2nd trip was planned 6 months before she was conceived and was combined with a
Disney cruise, and the 1st trip all our family and friends were going so we thought, "Why not?" We had a great time, it was so easy and I'd do it again in a second. My daughter wasn't exactly an easy baby at home, but in Disney she was wonderful.
The problems with her were that at home she needed to always be held (she slept in her own bed at night, but that was the only time she'd be alone). Well that's not always possible at home cause there are things to do, but at Disney she was held all day (very rarely in her stroller) in the Baby Bjorn and she was the happiest baby in the world. She never cried once, during either trip. She was exclusively breastfed so I just nursed her when she was hungry/thirsty, which was about every 1.5-2.5 hours.
The trips were in late May (19-24) and June (7-21) so it was very, very hot at times, but we kept her shaded with a thin, white, receiving blanket and sunhat and very hydrated with breastmilk, and we took breaks in the AC a lot and she was fine. We're going back in 2 weeks (!!) and she'll be 13 months. I'm more worried about this trip actually since she wants to walk/run all the time now!