I'm reliably told that one of the 'experiences' on the Hogwarts Express will be an encounter with the dementors; including both visual and physical effects. (Think pre-chilled icy-cold air being used to flash-chill the cabin as the dementors approach).

It all sounds quite stunning.

I still don't have much news on the new feature attraction though, other than its name: Escape from Gringotts.