This does pose the question though, are people with 'undesirable' intentions actually gonna ask for a jump seat. I don't know how strong the doors are now, but surely if they wanna get in they're going to. On some a/c (read 737) it might actually prevent someone getting in the flight dec if there's an occupant in the jump seat. I used to love the jumpseats i got. Strapped in for takeoff (usually happened with a friendly irish airline) and stayed there till all the pax got off on the other side. Had an absolutely fantastic time, and the seat was more comfortable that in the back (except when i forgot the f/d roof was as low as it was and banged a couple of switches and c/b's)
(okay waiting for the beer bottles to come shooting on stage).