I'm hate to chime in with a scare story, but make sure you really trust the shipping company. Ask around for recommendations or some such tactic. I obviously didn't do my homework on that front and the two boxes that were clearly bike boxes (one containing my bike, one containing paintings made by friends) were stolen along the way and never arrived.

As for shipping my bike when travelling on holiday, I've just done the packing and re-assembly myself using the marking tips suggested by others and not had a problem.