I've had reservations ticketed by UA then reissued incorrectly by agents (I think it was LX) and then i was at the gate over an hour before departure with a reservation in hand. and they couldn't get the boarding pass to print (i assume a ticket reissue issue) and then i watched board and fly home without me. was super super annoyed. except. it was a mileage ticket. they took about 2 more hours then got me booked the next day and at least i earned award miles for a business class flight on LX. that was how i justified to myself to not go totally crazy on them.