I've never lost a ticket yet, and even then, provided that I have the ticket number recorded (e.g. even if there is at least one reservation made with the ticket number in the PNR) then I can get the ticket reissued for a small fee. Sure this would be a hassle, but its do-able, and given that I have never lost a paper ticket in my life I reckon the risk is a small one.

But I do see pros and cons - I'm just old-fashioned enough to like something in my hand. It's also much easier to, for example, point to the list of airlines that the ticket is explicitly valid on when doing a last minute switch of airlines on a route than it is to try to debate with someone about something on a screen which only they can see. As an example, a few months back I was at LAX waiting for the AA flight to London. About 4 hours before departure they switched to coffins; I therefore wanted to switch to BA, which went in 3 hours. It seems to me that rolling up to the BA desk with a paper ticket saying "VALID ON ... BA..." was far less hassle than trying to get them to look at a (CX-issued) e-ticket would have been.