We have not...yet. My kids are 2 and 5, they go to bed very early and rise very early. They occasionally stay up later due to a special occasion but they never sleep later in the morning as a result, so they end up with a net total of less sleep than usual, which isn't great for their behavior. We are headed to WDW this summer and I'm considering letting the 5 year old watch the fireworks if she can stay up late enough, but that's only an option b/c we are staying at a monorail resort and we'll be able to view from the resort. I wouldn't want to keep them in the parks that late and deal with the crowds and slow exit on top of everything.