One reason we won't take the kids on a cruise yet (well, not on Royal Caribbean anyway) is that the railings have horizontal bars...perfect for kids to climb up on to lean over the railing. I just know my children would do that. Maybe not yours, but mine would.
I was heading to my Yahoo email, when a heading in the Yahoo news caught my eye. A 15 month old toddler was being held by his mother in the Toronto airport, she got distracted with her other son, and the toddler wiggled loose--over the railing, fell 15m, and sadly died. This might sound like an accident, but it was preventable. Simple babywearing could have prevented this. The next option would be the 'traditional' stroller. I have such a fear of this sort of thing happening to my own children, and I don't have either safety method anymore (I also don't, generally, hold any of my children on my hip anymore either). The next time you lift your child up to see something, think about this little boy.