For the last ten years, I have presumed that any evacuation (before departure/after landing or emergency land and de-camp) would be a riot.
I presume that the overwing doors, if relying on Pax, will not be opened properly or in a timely fashion.
I presume the worst will happen so that, if I find myself in such a circumstance, I hope to be pleasantly surprised.
Reading about the evacuation of the Costa Concordia, has only served to confirm my pessimism.