I agree with you "Lost in Saigon",many pilots do jumpseat, depends on the country, in the USA is a common practice (perhaps since 9/11 jumpseating is more difficult), in Italy they do sometimes, in Spain they do it all the time, even cabin crew are allowed to jumpseat in most spanish airlines (except Iberia).
in UK and France based companies it is not possible to jumpseat unless you are an employee, and even then is difficult. Some companies do allow jumpseat but you can't show at the gate at the last minute, you are asked to go to their ops office and ask for a jumpseating ticket.
Some crews will let in any pilot in, even showing up at the very last moment (a pilot just arrived in another plane and has not enough time to get through boarding and gets a lift through platform from ground personnel, i did it a couple of times get in like this)
It would be a good idea doing a list of companies that do allow jumpseating and conditions to do so.