I've had a couple of weird experiences, one on a ride and one off. The one that was on the ride was on Spiderman at USF, the ride started off normally but then about half way through the audio wasn't synced with the screen so it become quite strange on the drop scene hearing things after they had happened on the screen. Although it seemed fairly obvious to us, we were the only ones who complained and we got free fast passes from it so we weren't bothered!
The second one happened at Thorpe Park, we were watching Storm Surge and you can pay to use the water cannons to wet people but clearly someone didn't want to pay as he had brought his own supersoaker, so for 10 minutes we just watched him soaking everyone on the ride!