DD has only been once so far. She did have a couple "moments" last year, but nothing major. (Mostly just a few whining sessions, which we were able to curtail.)
The worst was in Epcot when she had a Princess costume on for lunch with the Princesses in Norway. It was about 10:30 in the morning, we'd just gotten to the park, and were headed to Soarin'. She started melting down--the costume was itchy, it was bothering her, she was too hot, it was rubbing, etc.
This was, of course, AFTER getting ready in the morning at the hotel, when I had tried to convince her to wear normal clothes to the park and take along the costume, but she refused. (In hindsight I should have brought along normal clothes anyway, but well, I didn't.)
So anyway. I am a parent who tends to believe in kids making their own decisions (within reason) and reaping the consequences of those decisions (again within reason). So she had made a decision to wear this dress, and the consequence was that she was now uncomfortable. No, I was NOT going to leave the park and punish all of us because of that. I was NOT going to remove her back to the room just so some people would not have to listen to her tantrum.
I did wait until she had pulled herself together enough BEFORE entering the Soarin' queue, so that all those people in the queue wouldn't be stuck with a trantrum-ing 5-year-old in very close proximity. However we did let her play it out.
For the people who get upset at parents "ignoring" their children's tantrums, all I can say is that this IS a form of parenting. When my DD gets in a certain mood, she will feed off ANY attention directed her way and just escalate it worse. You can do consquence after consequence after consequence and she still will not stop, it just gets worse. There are certain times where the best parenting for her IS to just ignore it and let her de-escalate it herself.
Now certainly I would apologize if she was really impacting someone else. Certainly I woudl remove her from a quiet show or a line (or not get in the line, as above) if she were doing a full-out tantrum.
That being said, I also think it's a bit unreasonable to expect to go to a place like WDW and think you'll never have to be confronted with a crying child. I'll do my best to not let my crying child impact you... but by the same token I'd like the people around us to not judge us for having a crying child!
(Although to be honest, if someone is judging us, I'm not likely to notice because am usually focused on DD at that point.)
If there is one thing I've learned as a parent, it's that kids will melt down occasionally... that kids go through stages and often outgrow their own behaviors... and that trying to maintain 100% control is unrealistic (and often counterproductive). Even with allowing DD to set our pace, to choose what we were doing 90% of the time (we went to MK five out of six park days, and yes, she got to choose what rides most of the time no matter where we were.... she and I did Barnstormer and Teacups I don't know HOW many times)... even with all that, there will be meltdowns and bad behavior... but it's not the end of the world.