Originally Posted by sheepstealer
I think you'll find contention on this point but IMO I think doing one will definitely help the other.
I was skiing for six or seven years until I switched over to snowboarding when I was 12 years old. Haven't looked back since.
I was a little ripper on my skis and I can honestly say that skiing most definitely helped me learn how to ride better. Balance and edge control if anything.
I don't think you're really answering the OP's question. I totally agree with you that doing one first (either one) will make it easier to learn the other afterwards. But the OP seems to be asking about learning both or doing both at the same time, and whether that will help either one.
I don't think it will personally. Time spent skiing is time not spent snowboarding. Yes, time spent skiing is still time spent learning how to handle lifts, edges, types of snow, etc, but you won't learn the "common" stuff any faster than you would on a snowboard.
I do think it's a good idea to know how to do both, but there's no speed-of-learning advantage.