From KLM online checkin:
"You have entered your preference for an exit seat.
To sit in an exit seat, you must be willing and able to assist in the event
of an evacuation.
Does any of the following apply to you?
* You are traveling with a child younger than 13 years of age.
* You are unable to hear or understand instructions given by the crew members
in English or Dutch.
* You have a condition that might prevent you from performing your evacuation
functions or that might injure you while performing such functions."
And my sincere apologies, Paxboy
Would this be the right point to state I don't completely agree with Techman? In reality training is the most most airlines have to go on but no amount of training stops certain people panicking; it just helps. I was once H&S officer in a large hotel for a few years and I've seen trained staff go to jelly and untrained customers solid as a rock in false alarm and real emergencies (e.g. 3am evacuations due to an actual fire).
But of course airlines should assume that their trained staff have an advantage. They also need to use all the information they can get about everyone else on board and a lot of it is right in front of their eyes. All airlines should do the above both at check-in and in the aircraft, where someone about whom there is any substantial doubt as to their physical aptitude in an emergency should be politely assisted to reseat themselves away from an emergency row. Yes, even if they've paid for the privilege. From a risk assessment perspective that's a no-brainer.