I'm used to e-tickets. Sometimes they are not the best things (especially when you are trying to change a chancelled flight and the idiot at the counter says "I need a copy of the ticket... well, it's electronic stupid it's in the computer!")

My only concern is that I have a reservation to get on a plane. It can be a paper, e-ticket or printed on a satin sheet as long as I can get on the plane!

But I follow ANNAS's advice: for international I alwasy ask for paper. London I went e-ticket with no problems but some countries I want written proof.